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ISBN 978-952-62-1278-4 (Paperback)ISBN 978-952-62-1279-1 (PDF)ISSN 0355-3191 (Print)ISSN 1796-220X (Online)

U N I V E R S I TAT I S O U L U E N S I SACTAA

SCIENTIAE RERUM NATURALIUM

U N I V E R S I TAT I S O U L U E N S I SACTAA

SCIENTIAE RERUM NATURALIUM

OULU 2016

A 679

Terhi Suoranta

ADVANCED ANALYTICAL METHODS FOR PLATINUM GROUP ELEMENTSAPPLICATIONS IN THE RESEARCH OF CATALYST MATERIALS, RECYCLING AND ENVIRONMENTAL ISSUES

UNIVERSITY OF OULU GRADUATE SCHOOL;UNIVERSITY OF OULU,FACULTY OF SCIENCE

A 679

ACTA

Terhi Suoranta

A C T A U N I V E R S I T A T I S O U L U E N S I SA S c i e n t i a e R e r u m N a t u r a l i u m 6 7 9

TERHI SUORANTA

ADVANCED ANALYTICAL METHODS FOR PLATINUM GROUP ELEMENTSApplications in the research of catalyst materials, recycling and environmental issues

Academic dissertation to be presented with the assent ofthe Doctoral Training Committee of Technology andNatural Sciences of the University of Oulu for publicdefence in the OP auditorium (L10), Linnanmaa, on 12August 2016, at 12 noon

UNIVERSITY OF OULU, OULU 2016

Copyright © 2016Acta Univ. Oul. A 679, 2016

Supervised byProfessor Paavo PerämäkiDoctor Matti Niemelä

Reviewed byProfessor Maria BalcerzakDoctor Douglas Baxter

ISBN 978-952-62-1278-4 (Paperback)ISBN 978-952-62-1279-1 (PDF)

ISSN 0355-3191 (Printed)ISSN 1796-220X (Online)

Cover DesignRaimo Ahonen

JUVENES PRINTTAMPERE 2016

OpponentProfessor Sebastien Rauch

Suoranta, Terhi, Advanced analytical methods for platinum group elements.Applications in the research of catalyst materials, recycling and environmentalissuesUniversity of Oulu Graduate School; University of Oulu, Faculty of ScienceActa Univ. Oul. A 679, 2016University of Oulu, P.O. Box 8000, FI-90014 University of Oulu, Finland

Abstract

Platinum group elements (PGEs) have a high commercial value and variety of applications indifferent fields of industry. One of the well-known applications is the use of palladium, platinumand rhodium in the catalytic converters of automobiles to reduce the amount of harmful gasesemitted to the environment. Advanced analytical methods are needed to deal with issues related todevelopment of new catalyst materials, recycling of PGEs from spent materials and for monitoringPGE emissions to the environment.

In the first part of this study the emphasis was on the catalyst materials. Especially, reliabledetermination of ruthenium content in catalyst materials required further studies. Consequently,acid digestions in closed vessels using a microwave oven or high pressure asher were comparedwith a previously reported fusion method. Furthermore, the recovery of PGEs from spent materialsis important due to many factors, for example, the high value of these metals, environmentalaspects related to their production and possible availability issues in the future. Thus, utilizationof microwave-assisted leaching and cloud point extraction (CPE) for the recovery of palladium,platinum, rhodium and ruthenium from catalyst materials was investigated.

The second part of this study concentrated on the PGEs in environmental samples and theanalytical challenges related to PGE determinations with inductively coupled plasma massspectrometry (ICP-MS). Due to the use of PGEs in catalytic converters of automobiles, they areemitted to the roadside environment. The use of Pleurozium schreberi, a terrestrial moss, foractive biomonitoring of these emissions was evaluated. Advanced analytical methods were neededto perform interference-free determinations of palladium, platinum and rhodium in these samples.Two alternative approaches for interference elimination were studied. Firstly, the interferingelements were removed using CPE as a chemical separation method. Secondly, interferences wereeliminated using ammonia as a reaction gas with the novel ICP-MS/MS (inductively coupledplasma tandem mass spectrometry) technique.

Keywords: catalyst material, cloud point extraction, environmental sample, ICP-MS,ICP-MS/MS, interference elimination, moss, platinum group elements

Suoranta, Terhi, Platinaryhmän alkuaineiden uudet analyysimenetelmät ja niidenhyödyntäminen katalyyttimateriaalien, kierrätysmahdollisuuksien jaympäristönäytteiden tutkimuksessa. Oulun yliopiston tutkijakoulu; Oulun yliopisto, Luonnontieteellinen tiedekuntaActa Univ. Oul. A 679, 2016Oulun yliopisto, PL 8000, 90014 Oulun yliopisto

Tiivistelmä

Platinaryhmän alkuaineita hyödynnetään monissa teknisissä sovelluksissa. Yksi tunnetuimmistaon autoliikenteen haitallisten päästöjen vähentäminen käyttäen palladiumia, platinaa ja rodiumiaautojen pakokaasukatalysaattoreissa. Luotettavia analyysimenetelmiä tarvitaan esimerkiksi kehi-tettäessä uusia katalyyttimateriaaleja, kierrätettäessä platinaryhmän alkuaineita käytetyistä mate-riaaleista tai seurattaessa platinaryhmän alkuaineiden määrää ympäristössä.

Tämän tutkimuksen ensimmäinen osa liittyi katalyyttien ruteniumpitoisuuksien määrittämi-seen ja platinaryhmän alkuaineiden kierrätykseen katalyyttimateriaaleista. Erityisesti näytteen-hajotusvaihe aiheuttaa usein ongelmia ruteniummäärityksissä. Tämän vuoksi tutkimuksessa ver-rattiin keskenään mikroaaltotekniikalla tai korkeapainetuhkistimella suoritettuja happohajotuk-sia ja aiemmin raportoidulla sulatemenetelmällä suoritettuja hajotuksia. Mikroaaltoavusteistaliuotusta sovellettiin yhdessä samepisteuuton kanssa tutkittaessa katalyyttimateriaalien palla-diumin, platinan, rodiumin ja ruteniumin kierrätysmahdollisuuksia. Aihe on ajankohtainen, kunhuomioidaan platinaryhmän alkuaineiden korkea hinta, niiden tuotantoon liittyvät ympäristöasiatsekä saatavuuteen liittyvät epävarmuustekijät.

Tutkimuksen toisessa osassa keskityttiin ympäristönäytteisiin ja erityisesti niiden ICP-MS -analytiikan (induktiiviplasmamassaspektrometria) haasteisiin. Autojen katalysaattoreista lähtöi-sin olevia platinaryhmän alkuaineita päätyy ympäristöön lähinnä teiden varsille. Näitä päästöjäarvioitiin aktiivista biomonitorointia käyttäen. Spektraaliset häiriöt vaikeuttivat kerättyjen sam-malnäytteiden (Pleurozium schreberi) palladium-, platina- ja rodiumpitoisuuksien määrityksiä.Tämän vuoksi mittauksissa esiintyvien häiriöiden poistossa hyödynnettiin kahta eri lähestymis-tapaa. Näistä ensimmäisessä häiritsevät alkuaineet poistettiin kemiallisen erotusmenetelmän,samepisteuuton, avulla. Toisessa tavassa häiriöt poistettiin uudella ICP-MS/MS -tekniikalla(induktiiviplasmatandemmassaspektrometria) käyttäen ammoniakkia reaktiokaasuna.

Asiasanat: häiriönpoisto, ICP-MS, ICP-MS/MS, katalyyttimateriaali, platinaryhmänalkuaineet, samepisteuutto, sammal, ympäristönäyte

7

Acknowledgements

This study was carried out at the University of Oulu in the Research Unit of

Sustainable Chemistry (former Department of Chemistry) within the research

group of Inorganic Analytical Chemistry during the years 2012–2016. Financial

support is gratefully acknowledged from the following groups: the Advanced

Materials Doctoral Program, the University of Oulu Graduate School, the Finnish

Cultural Foundation’s North Ostrobothnia Regional Fund, the Finnish Cultural

Foundation’s Central Fund, the Tauno Tönning Foundation and the Alfred Kordelin

Foundation’s Gust. Komppa Fund.

I am grateful to my supervisors, Professor Paavo Perämäki and Dr. Matti

Niemelä, for their guidance during these years. All the discussions, ideas and

practical advice were a great help. I wish to thank my follow-up group, Professor

Eero Hanski, Dr. Satu Ojala and Dr. Juha Piispanen for their advice and

encouragement. The reviewers of this thesis, Professor Maria Balcerzak (Warsaw

University of Technology) and Dr. Douglas Baxter (ALS Scandinavia AB), are

acknowledged for their valuable comments. I would also like to thank Aaron

Bergdahl for the English language revision of this thesis.

This work greatly benefited from the expertise of my co-workers. Many thanks

to Dr. Jarmo Poikolainen and Dr. Juha Piispanen (Natural Resources Institute

Finland) for co-operation with the biomonitoring studies. I am grateful to the Chair

of General and Analytical Chemistry, Montanuniversität Leoben for hosting my

researcher visit and for providing me access to their research facilities. Special

thanks to Professor Thomas Meisel for sharing his knowledge, enthusiasm and

positive attitude. Syed Nadeem Hussain Bokhari is acknowledged for his hard work

during our collaboration in Leoben. Our exchange student Oihane Zugazua

(University of the Basque Country) is acknowledged for helping with the

laboratory work related to the recycling experiments. I also wish to thank Seija

Liikanen and Päivi Vesala for their help with sample digestion and analysis in the

Trace Element Laboratory.

I would like to thank my colleagues in the research group of Inorganic

Analytical Chemistry – Heidi, Johanna and Matti – for introducing me to the

scientific world. Sharing the office with you was a huge advantage for my research

and I truly appreciate all the scientific and non-scientific conversations we had.

8

I would like to express my warmest thanks to my family and friends for their

support. Finally, Tuomas, thank you for always being there and trying to understand

the challenges of doctoral studies.

Oulu, May 2016 Terhi Suoranta

9

Abbreviations and symbols

2-MBT 2-mercaptobenzothiazole

AAS Atomic absorption spectrometry

BCR Community Bureau of Reference, the former reference materials

program of the European Commission

CPE Cloud point extraction

CPT Cloud point temperature

ETAAS Electrothermal atomic absorption spectrometry

EU European Union

HPA High pressure asher

ICP-MS Inductively coupled plasma mass spectrometry

ICP-MS/MS Inductively coupled plasma tandem mass spectrometry

ICP-OES Inductively coupled plasma optical emission spectrometry

ICP-SFMS Sector field inductively coupled plasma mass spectrometry

ICP-QMS Quadrupole inductively coupled plasma mass spectrometry

L/S ratio Liquid-to-solid ratio

MW microwave

NIST National Institute of Standards and Technology

PGEs Platinum group elements

PGMs Platinum group metals

RAF Relative accumulation factor

sd Standard deviation

Triton X-100 t-Octylphenoxypolyethoxyethanol

w mass fraction (µg kg-1)

XRF X-ray fluorescence spectrometry

10

11

List of original publications

This thesis is based on the following publications, which are referred to throughout

the text by their Roman numerals:

I Suoranta T, Niemelä M & Perämäki P (2014) Comparison of digestion methods for the determination of ruthenium in catalyst materials. Talanta 119: 425–429.

II Suoranta T, Zugazua O, Niemelä M & Perämäki P (2015) Recovery of palladium, platinum, rhodium and ruthenium from catalyst materials using microwave-assisted leaching and cloud point extraction. Hydrometallurgy 154: 56–62.

III Suoranta T, Niemelä M & Perämäki P (2014) Cloud point extraction of platinum group elements and gold: elimination of nitric acid-related problems with sulphamic acid. Anal Methods 6: 9321–9327.

IV Suoranta T, Bokhari SNH, Meisel T, Niemelä M & Perämäki P (2016) Elimination of interferences in the determination of palladium, platinum and rhodium mass fractions in moss samples using ICP-MS/MS. Geostand Geoanal Res DOI 10.1111/ggr.12116.

V Suoranta T, Niemelä M, Poikolainen J, Piispanen J, Bokhari SNH, Meisel T & Perämäki P (2016) Active biomonitoring of palladium, platinum, and rhodium emissions from road traffic using transplanted moss. Environ Sci Pollut Res DOI 10.1007/s11356-016-6880-1.

The present author conducted most of the experimental work related to Papers I,

III, IV and V. Part of the experimental work for Papers IV and V was carried out in

co-operation with Syed Nadeem Hussain Bokhari and prof. Thomas Meisel during

a research visit to Montanuniversität Leoben (Austria). The experimental work for

Paper II was mostly performed by Oihane Zugazua in supervision of the present

author. The present author wrote the first drafts for the papers and finalized them

with the co-authors.

12

13

Contents

Abstract

Tiivistelmä

Acknowledgements 7 Abbreviations and symbols 9 List of original publications 11 Contents 13 1 Introduction 15

1.1 Platinum group elements (PGEs) ............................................................ 15 1.2 Recycling of PGEs .................................................................................. 16 1.3 Environmental aspects ............................................................................ 17 1.4 Analytical methods ................................................................................. 18

1.4.1 Catalyst materials ......................................................................... 20 1.4.2 Environmental samples ................................................................ 20

2 Aims of the research 25 3 Materials and methods 27

3.1 Samples and reference materials ............................................................. 27 3.2 Sample preparation ................................................................................. 28

3.2.1 Devices ......................................................................................... 28 3.2.2 Digestion/leaching of PGEs ......................................................... 29 3.2.3 Cloud point extraction .................................................................. 30

3.3 Instrumentation ....................................................................................... 31 4 Results and discussion 33

4.1 PGEs in catalyst materials ....................................................................... 33 4.1.1 Digestion of Ru in catalyst materials [I] ....................................... 33 4.1.2 Leaching and recovery of Pd, Pt, Rh and Ru [II] ......................... 34

4.2 PGEs in the environment ........................................................................ 38 4.2.1 Elimination of spectral interferences in the determination

of PGEs [III, IV] ........................................................................... 38 4.2.2 Active biomonitoring of Pd, Pt and Rh with moss [V] ................. 46

5 Conclusions 51 References 55 Original publications 67

14

15

1 Introduction

1.1 Platinum group elements (PGEs)

Palladium (Pd), platinum (Pt), rhodium (Rh), ruthenium (Ru), iridium (Ir) and

osmium (Os) are known as platinum group elements (PGEs) or platinum group

metals (PGMs). High melting points, inertness to chemical attack, and catalytic

activity are examples of properties these six transition elements have in common

[1, 2]. Classification of PGEs to ‘noble metals’ or ‘precious metals’ with gold and

silver further highlights the high commercial value of these elements.

PGEs have applications in automobile, chemical, electrical, petroleum, glass

and medical industries [2, 3]. In addition, PGEs are used in jewelry and are traded

in the investment sector. To give a general overview; the applications are dominated

by Pd and Pt and to a lesser extent by Rh [3]. These three elements are most

commonly used in catalytic converters of automobiles to convert carbon monoxide,

nitrogen oxides and hydrocarbons to less-harmful products (e.g., water, carbon

dioxide and nitrogen). In addition, Pd and Pt serve as catalysts in production of

chemicals and pharmaceuticals. Also Ru is a versatile catalyst for chemical

reactions and has applications, for example, in Fischer-Tropsch synthesis and in

ammonia production [4]. In other than catalytic applications, PGEs have important

roles, for example, in electrical applications, such as multi-layer ceramic capacitors

(Pd) or hard disk drives (Pt, Ru) [2]. Furthermore, the Pt complex cisplatin is a

well-known anti-cancer drug [5].

PGEs are low in abundance in the Earth’s crust. Siderophilic (‘iron-loving’)

and chalcophilic (‘sulfur-loving’) PGEs are commonly associated with iron or

sulfur, but also with other metals (e.g., copper, tin, lead and bismuth) and metalloids

(e.g., arsenic, antimony, selenium and tellurium) [2, 6]. The primary sources of

PGEs are geographically concentrated in certain locations (e.g., South Africa,

Russia, North America and Zimbabwe) [7]. The Bushveld complex in South Africa

is the largest PGE deposit known and, thus, South Africa is the major producer of

PGEs, especially Pt and Rh [2, 3]. In addition, Russia is a major contributor to

worldwide Pd production [3].

Discussion on the availability of PGEs in the future has been going on due to

their high demand, limited availability and the environmental, social, economic and

political aspects related to PGE production [7–10]. For example, the European

Union (EU) has classified PGEs among critical raw materials [11, 12]. The main

16

reasons for this rating were the lack of primary production in EU countries, limited

recovery of PGEs from consumer products and limited substitution options for

PGEs by other metals in their applications [11].

1.2 Recycling of PGEs

In general, the recovery of PGEs from spent materials is viable due to their high

economic value and their availability in many secondary sources at relatively high

mass fractions when compared to primary sources [13–15]. Efficient collection of

the spent materials (especially catalyst materials), well-planned logistics and

modern refining methods play a crucial role in enhancing the recycling of PGEs

[13].

Pyrometallurgical and hydrometallurgical methods can be used to recover

PGEs from spent catalyst materials. In addition, gas phase volatilization methods,

such as carbochlorination, have been studied [16]. Pyrometallurgical methods are

commonly used on an industrial scale [17]. In pyrometallurgical processing, the

catalyst materials are smelted at high temperature (usually > 1500 °C) with suitable

fluxes. A liquid slag is formed, from which the PGEs are collected using a collector

metal (e.g., Cu or Fe) [18, 19]. Even though these methods are effective, they are

slow and energy consuming. In hydrometallurgical processing, suitable reagents,

such as acid or cyanide solutions are used in leaching of PGEs from recycled

materials, either directly, after pyrometallurgical processing or after other

pretreatment methods [15]. Hydrometallurgical processes consume less energy

than pyrometallurgical processes, but the recovery efficiencies tend to be lower and

generation of waste solutions may pose a problem [13, 20].

Recently, many studies have aimed at developing environmentally friendly

recovery methods for PGEs in spent catalyst materials using hydrometallurgical

methods. Because the formation of chloro complexes enhances the leaching of

PGEs, many methods are based on the use of hydrochloric acid. Where aqua regia,

the 1:3 mixture of concentrated nitric acid and concentrated hydrochloric acid, is

known to leach PGEs with good efficiency [21–23], the drawback is the formation

of gaseous compounds (e.g., NO), possibly harmful to the environment, during the

leaching process [15, 24]. To find more environmentally friendly leach solutions,

several reagents other than nitric acid – hydrogen peroxide [24], hydrogen peroxide

and sulfuric acid [25], cupric ions (Cu2+) [26] or electro-generated chlorine [27] –

have been tested to increase the oxidizing power of HCl-based leach solutions.

Alternatively, the use of cyanide- [28, 29] or iodine-based [30, 31] leach solutions

17

has been studied. Furthermore, attempts to use microwave (MW)-assisted leaching

in recovering PGEs from catalyst materials have been made [32, 33]. The results

have indicated that the leaching time could be significantly reduced by using MW-

assisted heating compared to conductive heating [32].

After initial dissolution of PGEs from catalyst materials, further refining to

separate PGEs from base metals or from each other has been reported, for example,

using precipitation methods [22, 32], extractions [22, 34–37], ion exchange [28, 38,

39] and biosorption [40]. Also, process waste solutions (e.g., from catalyst

impregnation processes) have been identified as a secondary source of PGEs.

Consequently, selective electrochemical recovery of Pd(II) from solutions

containing Rh(II) and Nd(III) has been studied [41].

1.3 Environmental aspects

Emissions of PGEs to the environment from metal production, catalytic converters

of automobiles and medical applications are known [42]. For example, a study

performed in the European arctic (in Finland, Norway and Russia) revealed the

emission of PGEs from the Russian nickel industry on the Kola Peninsula [43].

Furthermore, elevated mass fractions of PGEs have also been observed in remote

areas, indicating the presence of long-range transport of these elements [44, 45].

Catalytic converters of automobiles are often considered to be one of the main

sources of PGEs (Pd, Pt and Rh) in the urban environment [46]. PGE emissions

from road traffic have been monitored using several environmental materials: road

dust, soil, airborne particulate matter and plants [47]. Monitoring conducted over

time has shown an increase in the amounts of Pd, Pt and Rh in roadside soils in

Germany [48, 49]. Mass fractions exceeding the natural background values have

been determined also for Ir along major highways in Austria [50]. As long as the

effects of these emissions on human health and the environment are not well-known

[51], there is an obvious need to continue the monitoring efforts. So far, the amount

of PGEs in the environment has remained low and the possible adverse effects are

considered to be limited.

Among plants, the use of mosses for environmental monitoring has gained

popularity. For example, atmospheric deposition of heavy metals has been

monitored in European moss surveys at five-year intervals since 1990 [52, 53]. The

advantage of using mosses is that they obtain most of their nutrients from wet and

dry deposition, while the uptake of elements from soil is minimal. The monitoring

studies are performed either with naturally growing mosses (passive biomonitoring)

18

or mosses moved from an unpolluted area to the monitoring area (active

biomonitoring). The active biomonitoring approach, for example using the moss

bag technique [54], is beneficial especially in urban areas, in the vicinity of

industrial sources or in harsh environmental conditions (e.g., on slopes of volcanoes)

where natural vegetation is scarce [55–58]. When it comes to PGEs, studies have

indicated that mosses collect/retain higher amounts of PGEs than other plants [59–

61]. So far, biomonitoring studies for PGEs using mosses have been conducted in

European areas – European arctic [43], Finland [60, 62], Italy [63], Norway [64],

Austria [65] and France [66] – to monitor emissions related to traffic, urban area or

industry, chiefly by the means of passive biomonitoring (Table 1). Zechmeister et al. [67] recently summarized some important aspects related to planning of moss

biomonitoring studies for PGEs and the corresponding analytical methods: (i) Pt

has been determined more often that Pd or Rh, (ii) time-consuming methods of

matrix separation and PGE enrichment are needed for the interference-free

determination of PGEs by inductively coupled plasma mass spectrometry (ICP-

MS), especially with Pd and (iii) the use of Pleurozium schreberi or Hylocomium splendens was recommended for monitoring of PGEs.

1.4 Analytical methods

PGEs must be determined at highly variable levels in different sample types as

study aims may vary from the determination of active metals in catalyst samples

(in % range) to the determination of trace pollutants in environmental samples (in

µg kg-1 range). Consequently, a variety of instrumental techniques have been

applied for PGE determinations. For example, Ru contents in digested catalyst

materials have been determined using spectrophotometry [68–70], atomic

absorption spectrometry (AAS) [70–72] or inductively coupled plasma optical

emission spectrometry (ICP-OES) [73]. In addition, a non-destructive analytical

method, such as X-ray fluorescence spectroscopy (XRF), may be used if several

grams of sample material is available and suitable calibration materials can be

found [74].

19

Table 1. Summary of Pt, Pd and/or Rh biomonitoring studies with mosses [V].

Authors Location Year Element(s) Monitoring Moss species

Niskavaara et al. [43] European

arctic

2004 Pd, Pt Passive Hylocomium splendens, Pleurozium

schreberi

Niemelä et al. [60, 62] Finland 2004,

2007

Pt, Rh Passive Pleurozium schreberi

Beccaloni et al. [63] Italy 2005 Pd, Pt, Rh Passive Rhynchostegium megapolitanum,

Rhynchostegium confertum,

Eurhynchium praelogum,

Eurhynchium hians, Eurhynchium

speciosum, Scorpiurium circinatum

Reimann et al. [64] Norway 2006 Pt Passive Hylocomium splendens

Zechmeister et al. [65] Austria 2006 Pd, Pt, Rh Passive Pleurozium schreberi, Hylocomium

splendens, Scleropodium purum,

Hypnum cupressiforme, Abietinella

abietina

Active Hylocomium splendens

Ayrault et al. [66] France 2006 Pd, Pt Passive Cirriphyllum piliferum, Eurhynchium

speciosum, Physcomitrium

eurystomum, Pylasisia polyantha,

Rhacomitrium canescens,

Polytricum formosum,

Scleropodium purum

Active Scleropodium purum

Techniques offering lower detection limits; inductively coupled plasma mass

spectrometry (ICP-MS), electrothermal atomic absorption spectrometry (ETAAS)

or adsorptive stripping voltammetry are applied for the determination of PGEs in

environmental samples [75, 76]. Among these, ICP-MS is the most often used

technique for the determination of Pd, Pt and Rh. However, the determination,

especially with quadrupole ICP-MS (ICP-QMS), is hampered by isobaric and

polyatomic interferences, such as 106Cd+ for 106Pd+, 89Y16O+ and 88Sr16O1H+ for 105Pd+ or 206Pb2+ for 103Rh+ (Table 2). Analytical procedures used for the

determination of PGEs including sample digestion methods, separation/pre-

concentration procedures and/or instrumental techniques have been

comprehensively reviewed, for example, by Balcerzak [76, 77], Bencs et al. [75],

Godlewska-Żyłkiewicz [78] and Rao & Reddi [1]. Some aspects related to

pretreatment and analysis of catalyst materials and environmental samples are

discussed below.

20

Table 2. Potential interferences on Pd, Pt and Rh isotopes [IV].

Monitored m/z Isotope of interest Potential interfering species

103 103Rh 206Pb2+, 87Sr16O+, 87Rb16O+, 63Cu40Ar+, 66Zn37Cl+, 68Zn35Cl+

105 105Pd 89Y16O+, 88Sr16OH+, 65Cu40Ar+, 68Zn37Cl+

106 106Pd 106Cd+, 90Zr16O+, 89Y16OH+, 66Zn40Ar+

108 108Pd 108Cd+, 92Zr16O+, 92Mo16O+, 68Zn40Ar+

194 194Pt 178Hf16O+

195 195Pt 179Hf16O+

196 196Pt 196Hg+, 180Hf16O+, 180W16O+

198 198Pt 198Hg+, 181Ta16OH+, 182W16O+

1.4.1 Catalyst materials

In general, sample digestion in closed vessels is nowadays favored due to its many

advantages, such as shortened digestion times and limited amount of liberated

corrosive acid vapors. MW-assisted acid digestion methods for the determination

of Pd, Pt and Rh in catalyst materials have been recently studied [33]. Ru contents

in catalyst materials are often determined as a part of development of new Ru

catalysts, but only a few studies have focused on the reliable determination of Ru

in these materials [68–73]. In addition, none of these studies applied sample

preparation in closed vessels (e.g., MW-assisted digestions). Instead, a fusion

method employing KOH and KNO3 was applied in one of the studies [70] and acid

digestions on a hot plate were carried out in the others.

There are also some additional details to be considered in Ru analytics. The

main challenges in Ru determinations are the resistivity of (metallic) Ru to acid

attack and the possible formation of volatile RuO4 under oxidizing conditions [74].

For example, the volatilization of Ru in boiling nitric acid solutions has been

noticed to be faster with increasing acid concentration [79, 80]. Consequently, a

higher hydrochloric acid to nitric acid ratio than in aqua regia (e.g., 6:1 vs. 3:1) has

been recommended for Ru digestions [68, 74]. This modification has been

concluded to give either slightly better [68] or similar [72] results when compared

to aqua regia in the determination of Ru in carbon-supported Pt-Ru catalysts.

1.4.2 Environmental samples

In environmental samples, the concentrations of PGEs are very low and especially

spectral interferences (Table 2) may cause serious systematic errors during

21

determinations. Therefore interference correction, elimination and minimization

methods have a crucial role in the determinations of PGEs in environmental

samples by ICP-MS. In some cases (e.g., with 195Pt), the interferences can be

avoided directly by using a high-resolution sector field ICP-MS (ICP-SFMS) [81].

On the contrary, resolving the 89Y16O+ interference in 105Pd+ determinations would

require a resolution (m/∆m) of 27 600 [81], whereas the highest practical resolution

of many ICP-SFMS instruments is around 10 000 [82, 83]. Combinations of

different methods have often been used to improve the accuracy of the results. In

many cases mathematical correction methods have been employed. However, they

are often insufficient for resolving interferences in Pd determinations [62, 84–87]

and they tend to increase the uncertainty of the corrected results [88].

Chemical separation methods have been used to separate PGEs from

interfering elements prior to ICP-MS determination. Ion exchange methods, based

on the separation of anionic PGE chloro complexes from the cationic species

formed by the interfering elements, have often been applied. Ion exchange is mostly

performed off-line prior to ICP-MS determination [89–96], but also on-line

coupling with ICP-MS has been successfully used [50, 97, 98]. Both cation

exchange resins used to retain the interfering elements [50, 90, 93, 95, 97] and

anion exchange resins used to retain PGEs (for later elution) [89, 98] have been

applied. It must be noted, that some interfering elements, such as Hf and Zr may

also form anionic complexes [99]. To eliminate these interferents, multi-stage

interference removal methods have been applied. For example, columns packed

with complexing agents [91, 94, 96] have been used for this purpose.

In addition to ion exchange methods, also preliminary acid leaching of the

interfering elements [88], co-precipitation of PGEs with Te or Hg [60, 94, 100–102]

and extraction methods [59, 84, 88, 103, 104] have been used to remove

interferences in PGE determinations in environmental materials. Among extraction

methods, cloud point extraction (CPE), applied to PGE determinations in road dust

samples [88, 103, 104], is an interesting alternative for interference elimination. In

CPE, neutral (hydrophobic) compounds formed between the analytes and an added

complexing agent are extracted to micelles formed by an added surfactant. Further,

the surfactant-rich phase is separated from the aqueous phase by heating the system

above its cloud point temperature (CPT) (Fig. 1). The CPE system is quite flexible

as the properties (e.g., CPT, extraction efficiency, selectivity, etc.) are dependent on

the selected extraction conditions including, for example, the surfactant and its

concentration, extraction temperature and time, pH, ionic strength and the nature

of the complexing agent [105, 106]. CPE offers several benefits: low cost, simple

22

procedures, high pre-concentration factors and environmental safety [107]. Even

though CPE is not yet widely used in PGE determinations in environmental

samples, a variety of other applications for inorganic analytes have been published,

especially during the past decade. These applications during the time period of

2004–2011 have been reviewed by Ojeda and Rojas [108, 109].

Fig. 1. A schematic presentation of cloud point extraction (CPE): (1) addition of reagents

to the sample solution; (2) clouding of the sample solution, extraction of the PGE

complexes to micelles of the surfactant; (3): separation of the surfactant-rich phase

from the sample solution.

Although effective, chemical separation methods tend to be time-consuming. To

avoid this, instrumental interference elimination methods have also been used. For

example, desolvating sample introduction systems have been applied for reducing

oxide interferences in ICP-MS determinations [65, 93, 110, 111]. Also, a variety of

collision/reaction gases has been used to reduce the interferences during ICP-MS

determination of PGEs. For example, helium was used in minimizing molecular

interferences after Hg-coprecipitation [102], oxygen was used in reducing oxide

interferences (by oxidation of the interfering elements to higher oxides) [112],

ammonia was used for removal of HfO+ interference in Pt determination [113] and

hydrogen was used to avoid argon-based interferences (e.g., 40Ar63Cu+ on 103Rh+

and 40Ar65Zn+ on 105Pd+) after fire assay sample pretreatment [48].

The introduction of the novel ICP-MS/MS (inductively coupled plasma tandem

mass spectrometry) instrumental set-up has provided new opportunities for

interference removal using collision/reaction gases (Fig. 2). The use of a

quadrupole analyzer before the collision/reaction cell minimizes the possibility of

forming new interferents via side reactions. So far, there are only a few applications

23

of ICP-MS/MS for environmental sample materials. The technique has been used

to remove interferences in the determination of iodine in soil samples [114] and As

and Se in reference materials of plant, animal and environmental origin [115].

Among other sample materials, for example, the interference-free determination of

S in organic matrices [116], P, S and Si in diesel and oils [117], Ti in blood serum

[118], Se in serum samples [119] and As and Se in foodstuff [120] using ICP-

MS/MS have been studied. Furthermore, the removal of interferences in PGE

determinations has been studied using geological reference materials [121–124]

and matrix-free standard solutions [125]. According to a recent review by Balcaen

et al. [126], the popularity of the ICP-MS/MS technique can be expected to increase

in the future.

Fig. 2. A simplified illustration of the elimination of spectral interferences in the

determination of 103Rh with the ICP-MS/MS technique by using ammonia as a reaction

gas.

24

25

2 Aims of the research

The main objective of this research was to develop analytical methods for the

determination of PGEs in catalyst materials and environmental samples to enhance

the research of catalyst development and environmental issues. In addition,

recovery of PGEs from catalyst materials was studied. The key aims of this research

were:

1. To achieve a complete digestion of Ru in catalyst materials. For this purpose

different digestion methods were compared. [I]

2. To develop environmentally friendly methods for the recovery of Pd, Pt, Rh

and Ru from catalyst materials, based on MW-assisted leaching and CPE. [II]

3. To develop a CPE method for the interference-free determination of PGEs by

ICP-QMS in samples digested with aqua regia. [III, IV]

4. To investigate the feasibility of ICP-MS/MS technique in elimination of

spectral interferences in the determination of Pd, Pt and Rh in aqua regia

digested moss samples. [IV]

5. To evaluate the use of Pleurozium schreberi (a terrestrial moss) in active

biomonitoring of traffic-related PGE emissions. [V]

26

27

3 Materials and methods

3.1 Samples and reference materials

Four commercially available Ru-catalysts were used in comparing the digestion

methods for Ru determinations [I]. The catalyst materials were 0.5% Ru on 3 mm

alumina tablets (Alfa Aesar), 2% Ru on 1/8 in. alumina pellets (Alfa Aesar), 5% Ru

on alumina (Aldrich) and 5% Ru on carbon powder (Engelhard). A sub-sample

taken from each catalyst material was ground prior to the comparisons to ensure

the homogeneity of the samples. The first of these catalyst materials, ground to a

particle size of less than 300 μm, was also used in the recycling studies [II]. In the

absence of certified reference materials for Ru in catalyst materials, Ru powder

(99.9%, –325 mesh, Alfa Aesar) and selected Ru compounds, RuO2·xH2O (99.99%,

Ru 54-54%, Alfa Aesar), anhydrous RuO2 (99.95%, Ru min. 75.2%, Alfa Aesar)

and anhydrous RuCl3 (99.5%, Alfa Aesar) were used to investigate the efficiencies

of the digestion methods in Paper I.

To study the emission of PGEs due to road traffic, moss samples (Pleurozium schreberi) were transplanted along highway E75 in co-operation with the Natural

Resources Institute Finland [IV, V]. The samples were transplanted to three

different locations and to three distances (2 m, 7 m and 12 m) from the highway.

The samples were collected after an exposure period of 105 days. In addition, five

background samples were collected from the original location of the mosses after

the same period. The last four annual growth sections (the green part of the moss)

were separated for analysis, air dried to a constant weight at 35 °C and ground. For

more details see Paper V.

Two certified reference materials were used in this study. NIST SRM 2557

(NIST, Gaithersburg, USA) is a used monolith automotive catalyst ground to a

particle size less than 74 μm. SRM 2557 with certified values of 1131 ± 11 mg kg−1

for Pt, 233.2 ± 1.9 mg kg−1 for Pd and 135.1 ± 1.9 mg kg−1 for Rh (± 99%

confidence interval) was used in recycling studies and to study the analytical

performance of the CPE method [II, III, IV]. Indicative values for Al (20 wt.%), Ce

(1.3 wt.%) and Zr (300 mg kg-1), among other matrix elements, are also given in

the certificate of this material. BCR-723 road dust (IRMM, Geel, Belgium) has

certified mass fractions of 6.1 ± 1.9 µg kg-1 for Pd, 81.3 ± 2.5 µg kg-1 for Pt and

12.8 ± 1.3 µg kg-1 for Rh. In addition, indicative values for many elements are listed

in the certificate. BCR-723 was used in studying the applicability of the CPE

28

method (ICP-QMS) and the ICP-MS/MS technique for the analysis of

environmental samples [IV, V]. A moss reference material M3 (P. schreberi, Finnish Forest Research Institute [127]) was used as an additional sample matrix at

the method evaluation stage [IV].

3.2 Sample preparation

Different sample preparation methods were utilized during this study. In general,

MW-assisted acid digestion procedures were most often used. Sample treatment in

a high pressure asher (HPA) was employed when comparison with higher

temperatures, longer digestion times and/or conductive heating was needed. In

addition, a fusion method was applied for Ru digestions. Furthermore, CPE was

used for removing interfering elements from the MW-digested sample solutions

prior to instrumental determination of PGEs.

3.2.1 Devices

A CEM MARS 5X microwave oven (CEM Corp.), operated in a temperature-

controlled mode, was used for MW digestions of the samples [I, III–V], for

leaching experiments on the catalyst materials [II] and for the optimization of CPE

[III]. XP-1500 plus high-pressure Teflon® TFM vessels (CEM Corp., 100 ml,

maximum pressure 10 MPa and temperature 300 °C) were used in the MW-assisted

digestions and leaching experiments. In CPE experiments, 50 mL polypropylene

centrifuge tubes, placed in 250 mL beakers (3 tubes in each beaker), were used

instead of the XP-1500 vessels. To control the extraction temperature in CPE

experiments, the temperature sensor was placed in one of the centrifuge tubes.

A Julabo TW8 water bath (Julabo GmbH) was used in recycling-related CPE

experiments, in reference extractions during the CPE method optimization [III] and

further in extractions of PGEs from environmental samples (moss, road dust) [IV].

An HPA-S (Anton Paar GmbH) high pressure asher with 90 mL quartz vessels was

used in studying the acid digestions of Ru samples [I]. Additionally, the HPA-S was

used for conductive heating of the catalyst samples in the recycling experiments

[II]. A programmable muffle furnace L5/11/B170 (Nabertherm GmbH) was used

for sample digestions with the fusion method [I].

29

3.2.2 Digestion/leaching of PGEs

MW-assisted digestions were performed prior to determination of Pd, Pt, Rh and/or

Ru in catalyst materials and environmental samples [I, III–V]. In addition, MW-

assisted leaching of PGEs for recycling purposes was studied [II]. A summary of

the MW-assisted methods is presented in Table 3. In brief, the experiments were

carried out using mixtures of conc. HCl and conc. HNO3, either 6:1 (v/v) or 3:1

(v/v, aqua regia) with a two-stage temperature program (stage 1 – heating to target

temperature at 15 min; stage 2 – holding at target temperature for 10 min). The

program was followed by a cool-down step.

Table 3. Summary of the MW digestions.

Sample material Sample mass Acid mixture Target temperature

Ru catalysts [I] 50–100 mg 10.5 mL of HCl-HNO3 (6:1)

or 10 mL of aqua regia

180 °C

Ru powder and Ru compounds [I] 5–10 mg 10.5 mL of HCl-HNO3 (6:1)

or 10 mL aqua regia

180 °C

Catalyst samples for recycling

studies [II]

100–1600 mg 8 mL of HCl or HNO3 or

aqua regia

120 °C (90–210 °C)

SRM 2557 (autocatalyst) [III] 5 mg 8 mL of aqua regia 180 °C

Moss samples [IV, V] 500 mg 8 mL of aqua regia 210 °C

BCR-723 (road dust) [IV, V] 250 mg 8 mL of aqua regia 210 °C

HPA digestions were applied for Ru catalysts (50–100 mg) and for Ru powder and

Ru compounds (5–10 mg) [I]. After adding 6 mL of HCl and 1 mL of HNO3 the

vessels were closed and inserted into the pressure chamber of the HPA. The system

was pressurized with nitrogen to 100 bar and a three-stage digestion program was

run (program: stage 1 – rapid heating to 100 °C; stage 2 – heating from 100 °C to

300 °C at 30 min; stage 3 – holding at 300 °C for 180 min). After the program, cool

down and depressurizing steps were needed. The HPA was also used to study the

leaching of Pd, Pt, Rh and Ru from catalyst samples (100 mg, 6 mL HCl and 2 mL

HNO3) using conductive heating [II]. A different temperature program (stage 1 –

heating to 120 °C at 15 min; stage 2 – holding at 120 °C for 10 min) was used in

this case to allow the comparison to the MW-leached samples.

A fusion method described by Taddia and Sternini [70] was applied for Ru

catalysts (50–100 mg) and for Ru powder and Ru compounds (5–15 mg) [I].

Carbon-supported catalysts were ashed prior to sample fusion. The fusion was

performed in nickel crucibles at 450 °C with 0.38 g KOH and 0.65 g KNO3. To

30

stabilize the formed Ru compounds (mainly RuO42-) during dissolution of the melts,

K2S2O8 and KOH were used. Further, the formed Ru compounds were converted

to stable chloro complexes (RuCl62-) using HCl.

3.2.3 Cloud point extraction

Different variations of a CPE procedure employing 2-mercaptobenzothiazole (2-

MBT, Fig. 3) as a complexing agent and Triton X-100 (t-octylphenoxy-

polyethoxyethanol, Fig. 3) as a surfactant [128, 129] were used in this study [II–

IV]. As a general scheme, Triton X-100 (as a 10% m/v solution in ultrapure water)

and 2-MBT (as a 1% m/v solution in 0.5 mol L-1 NH4OH) were added to sample

solutions in 50 mL centrifuge tubes. Additional reagents to promote the extraction

were added either before or after Triton X-100 and 2-MBT, depending of the role

of the additive. The samples were heated/extracted either in a microwave oven or

in a water bath. During the heating, a gravitational phase separation was achieved.

After the heating stage, the samples were cooled down and the aqueous phase was

decanted. The surfactant-rich phase was diluted with 1 mol L-1 HCl for instrumental

determination of PGEs.

Fig. 3. The structures of 2-mercaptobenzothiazole (2-MBT) and Triton X-100 (n=9–10).

In the first type of CPE experiments tin(II) chloride was used as an additive. This

type of CPE is suitable for sample solutions containing an HCl-based matrix. This

was the case with the recycling experiments [II]. A 10-mL aliquot of the sample

solution was taken for the centrifuge tube and diluted to 20 mL (approx. 1 mol L-1

HCl). Based on the optimization experiments 2 mL of Triton X-100 and 1 mL of 2-

MBT were added. Solutions were left to stand for 15 min and 1.5 mL of SnCl2

(10%, m/v SnCl2 in 6 mol L-1 HCl) was added. The extraction was performed in a

water bath (heating to 90 °C at 25 min and holding at 90 °C for 120 min). Tin(II)

chloride was tested also as an additive during the method optimization for samples

containing aqua regia [III]. Here, 2 mL of Triton X-100, 2 mL of 2-MBT and 0.5

mL of SnCl2 were added to 40 mL samples. The samples were extracted in open

31

tubes in a microwave oven (heating to 90 °C at 5 min and holding at 90 °C for 60

min) [129].

Sulfamic acid was introduced as a new additive for samples containing aqua regia. As a result of careful method optimization, 0.5 g of sulfamic acid was added

prior to 3 mL of Triton X-100 and 4 mL of 2-MBT to 40 mL sample solutions. The

samples were extracted in loosely capped tubes either in a microwave oven (heating

to 90 °C at 15 min, holding at 90 °C for 75 min) or in water bath (heating to 90 °C

at 25 min and holding at 90 °C for 120 min).

3.3 Instrumentation

ICP-OES and ICP-MS techniques were used for elemental analyses in this study.

Depending on the sample matrix, several elements other than PGEs were also

determined. Detailed descriptions of the parameters used in the measurements are

presented in Papers I–V. A general overview is given below.

A PerkinElmer Optima 5300 DV ICP-OES (PerkinElmer Inc.) was used in

determining Pd, Pt, Rh, Ru, Al, Ce and Zr in studies related to catalyst materials.

The ICP-OES was equipped with an AS-93plus auto sampler, a Ryton double-pass

Scott-type spray chamber and a Gem Tip Cross-flow pneumatic nebulizer. An

Agilent 5100 ICP-OES (Agilent Technologies) was used in determinations of Al,

Ba, Cr, Fe, Mn, Ni and V in environmental samples (moss, road dust). The

instrument was equipped with a Cetac ASX-520 autosampler (Cetac Technologies),

a glass cyclonic spray chamber and a concentric glass nebulizer.

A Thermo Elemental X7 quadrupole ICP-MS (Thermo Elemental) equipped

with a Cetac ASX-500 autosampler (Cetac Technologies), a standard low-volume

glass impact bead spray chamber (Peltier cooled at + 3 °C) and a concentric glass

nebulizer was used in the determination of Pd, Pt and Rh and other elements (Cd,

Ce, Co, Cu, Mo, Pb, Sb, Sr, Y, Zn and Zr) in environmental samples (moss, road

dust) and Au, Ir, Pd, Pt, Rh, Ru in standard solutions subjected to CPE.

An Agilent 8800 triple quadrupole ICP-MS (Agilent Technologies) was used

in the determination of Pd, Pt and Rh in environmental samples (moss, road dust)

by utilizing the collision/reaction cell technology combined with MS/MS

measurement at the Montanuniversität Leoben, Austria. The instrument was

equipped with a double-pass Scott-type spray chamber (Peltier cooled at + 2 °C), a

concentric glass nebulizer and ESI SC-FAST or ESI SC-4DX autosampler

(Elemental Scientific). Different gases were used in the reaction cell during the

analyses: O2 with a flow rate of 0.3 mL min-1, He with a flow rate of 4 mL min-1

32

and NH3 (10% NH3 in He) with flow rates of 2 mL min-1 and 3 mL min-1. An

additional gas flow of 1 mL min-1 He was used with NH3. 115In was used as an

internal standard in the ICP-MS/MS determinations.

33

4 Results and discussion

The study is divided into two parts for the ‘Results and discussion’ section. The

first part includes studies related to catalyst materials: determinations of Ru

contents in catalysts as well as the recycling-related studies. Catalyst materials have

a relatively high amount of PGEs present and, thus, ICP-OES was used for

elemental analysis. The second part focuses on analytical problems related to the

determination of low mass fractions of PGEs in environmental materials. ICP-MS

was used in analyses and the removal of interferences was carefully studied. Special

attention was paid to developing a CPE method capable of separating the PGEs

from interfering elements in aqua regia-digested samples. Furthermore, the

potential of the novel ICP-MS/MS technique in the elimination of spectral

interferences in PGE determinations was evaluated.

4.1 PGEs in catalyst materials

4.1.1 Digestion of Ru in catalyst materials [I]

A complete dissolution of Ru is a crucial step in analytical procedures for the

determination of Ru with measurement techniques using liquid samples (e.g., ICP-

OES). There is often a lack of information concerning the digestion method, when

Ru contents of catalyst materials are reported. As summarized in the Introduction

(1.4.1), there are a couple of special features related to Ru behavior during analyses.

On one hand, (metallic) Ru is known to be very resistant against acid attack and,

on the other hand, Ru may volatilize as RuO4 if the conditions are too oxidizing.

In this study, different digestion methods were compared for the determination

of Ru in alumina- and carbon-supported catalyst materials [I]. Acid digestions were

performed in closed vessels in a microwave oven (180 °C) or in an HPA (300 °C).

In addition, a fusion method with KOH and KNO3 was used [70]. An interesting

comparison between the digestion efficiencies of the methods was obtained using

Ru powder and Ru compounds possibly present in catalyst materials (RuO2·xH2O,

anhydrous RuO2 and RuCl3). The results are presented in Table 4. The fusion

method was successful in the digestion of all of the studied compounds, whereas

the acid digestion methods resulted in incomplete recoveries with three of the four

compounds. Only RuO2·xH2O was fully digested with acids. The HPA method,

with higher temperature and longer digestion time, had higher digestion efficiencies

34

when compared to the MW methods. Furthermore, no difference between the acid

mixtures (3:1 vs. 6:1, HCl to HNO3) was observed in MW digestions of these

materials.

The same trends were not observed with the studied catalyst materials. Instead,

the results obtained with all of the methods were similar, indicating that Ru in these

catalyst materials was in an easy-to-dissolve chemical form. Thus, the MW

methods were well-suited to the studied catalyst samples. In addition, the speed and

simplicity of MW methods is a clear benefit over fusion and HPA. On the other

hand, as the results showed, MW methods may be vulnerable to the chemical form

of Ru. This might be a problem, for example, with thermally activated catalysts, as

easy-to-dissolve RuO2·xH2O might convert at least partially to RuO2 at high

temperatures [130]. Other factors possibly having an effect on the dissolution

behavior of Ru are the particle size and the dispersion of Ru (compounds) on the

surface of a support material [77]. Thus, when a digestion method for a particular

set of unknown catalysts is chosen, careful consideration together with a reliable

reference method should be used.

Table 4. Recoveries obtained for different Ru compounds (%, ± sd) using various

digestion methods (n=3) [I].

Compound Digestion method

Fusion HPA (6:1 HCl-HNO3) MW (6:1 HCl-HNO3) MW (aqua regia)

RuO2·xH2O 94 ± 2a 97 ± 1 100 ± 2 98 ± 1

Anhydrous RuCl3 96 ± 4b 84 ± 8 < 1 < 1

Ru powder 93 ± 4a 24 ± 2 < 1 < 1

Anhydrous RuO2 94 ± 2a < 1 < 1 < 1

a n=4, b n=7

4.1.2 Leaching and recovery of Pd, Pt, Rh and Ru [II]

The applicability of MW-assisted leaching and CPE for the recovery of Pd, Pt, Rh

and Ru from catalyst materials was also studied (Fig. 4). These methods were

considered to have potential for larger-scale use. The target was both to obtain good

recoveries for PGEs and to separate them efficiently from matrix elements (e.g., Al,

Ce and Zr).

Based on previous studies, MW-assisted heating was expected to speed up the

leaching processes of PGEs [32, 33]. In this study, leaching with HCl, HNO3 and

aqua regia was studied at five different temperatures (90, 120, 150, 180 and 210 °C).

35

Recoveries of over 78% were observed for Pd, Pt, Rh and Ru using the studied

method at 120 °C with aqua regia or HCl (Fig. 5, Fig. 6). The use of HNO3 alone

resulted in low(er) recoveries. For reference, the leaching of Pd, Pt and Rh with

HCl was also studied using conductive heating with an HPA. Using the same

temperature program, average recoveries from 6% to 35% were obtained. These

findings demonstrate that the procedure with MW-assisted heating has benefits.

Especially Rh has often been leached with lower efficiencies than Pd and Pt. The

good leaching efficiencies obtained in this study indicate that elevated temperatures

obtained in closed vessels and/or effects created by MWs, such as local

superheating of the leach solution or selective heating of the catalyst material [131],

favor the dissolution processes. Even higher, over 90% recoveries, were obtained

at a temperature of 150 °C in the microwave oven. However, by increasing the

temperature from 120 to 150 °C, a clear increase in the leaching of matrix elements,

for example Al (Fig. 5 and Fig. 6), was also observed.

Fig. 4. Flowsheet for the recovery of Pd, Pt, Rh and Ru in catalyst materials [II].

The effect of liquid-to-solid (L/S) ratio on the recoveries of PGEs was investigated

by performing the leaching at 120 °C with HCl. The tested L/S ratios ranged from

5 to 80, corresponding to sample masses from 1.6 to 0.1 g in 8 mL of HCl. Ru was

leached with good efficiency with all the L/S ratios used. Pd, Pt and Rh were

leached with good efficiencies with L/S ratios > 40, whereas the recoveries

decreased at ratios < 40. In addition, the repeatability of the leaching procedure was

poorer in the latter case. Even though the results indicate that these lower L/S ratios

may be useful, they point out that attention should be paid to studying other factors

36

as well, such as stirring during the heating stage or the duration of the heating. Also,

the use of a higher leaching temperature (> 150 °C) would probably result in better

recoveries.

Fig. 5. The recoveries (% ± sd) of Pd, Pt, Rh and Al after MW-assisted leaching of

catalyst material SRM 2557 at different temperatures (n=3) [II]. The recoveries were

calculated based on either certified (Pd, Pt, Rh) or indicative (Al) concentrations given

in the certificate of the material.

Fig. 6. The recoveries (% ± sd) of Ru and Al after MW-assisted leaching of catalyst

material 0.5% Ru on 3mm alumina tablets, at different temperatures (n=3) [II]. The

recoveries were calculated assuming that the material contained 0.5% of Ru and 99.5%

of Al2O3 (53% of Al).

37

CPE methods have been used in analytical chemistry with the aim of pre-

concentrating very low amounts of PGEs for instrumental determinations [103, 128,

129, 132]. Thus, CPE could have potential in recovering PGEs from leach solutions

and/or dilute waste solutions containing PGEs to ensure their complete recovery.

At the same time CPE, consuming low amounts of relatively environmentally

friendly reagents, could provide a method for the separation of PGEs from matrix

elements. According to our knowledge, the applicability of a CPE method for

recycling of Pd, Pt, Rh and Ru was evaluated for the first time in this study.

The selected CPE method, utilizing 2-MBT as a complexing agent and Triton

X-100 as a surfactant, had previously been used in analysis of Pt in concentrations

< 0.2 µg L-1 [129]. SnCl2 was used as an additive in the CPE method to accelerate

the ligand exchange processes (e.g., by changing the oxidation state of Pt) [128].

To use the method for recycling purposes, optimization to a much higher

concentration range (> 1 mg L-1) was necessary. Thus, a full two-level factorial

design (24) was used to study the effect of different PGE concentrations and to

optimize the amounts of reagents (Triton X-100, 2-MBT and SnCl2). A model based

on multiple linear regression was fitted to the experimental data using MODDE 9.1

(Umetrics) software. The outcome of this optimization step is presented in detail in

Paper II. To summarize, the amounts of Triton X-100 and SnCl2 in the samples had

to be increased due to the higher PGE concentration level. On the other hand, no

need to increase the amount of 2-MBT was observed, probably due to its presence

in high excess when compared to the PGEs. It must be noted that increasing the

amount of a certain reagent in CPE is not always advantageous; instead it may have

adverse effects on the properties of the CPE system, for example, via changing the

physical properties such as the viscosity of the surfactant-rich phase.

The optimized CPE method was applied to leach solutions (HCl concentration

1 mol L-1) of 0.2 g, 0.4 g and 0.8 g catalyst samples. The recoveries as well as the

concentration ranges of the PGEs and matrix elements in the sample solutions are

presented in Table 5. The recoveries obtained for Pd, Pt and Rh indicate that a CPE

step can be applied in the recovery of these metals from catalyst materials and/or

catalyst leaching waste solutions. Ru was extracted with lower recoveries, possibly

due to its higher concentration range when compared to Pd, Pt and Rh (9–40 mg L-

1 vs. 0.2–8 mg L-1) or due to chemical properties of Ru, such as hydrolysis of the

Ru complexes [74]. Less than 5% of the matrix elements remained after the

extraction step. The amount of matrix elements could be further reduced by

improving the removal of the aqueous phase. In the future, the recovery of PGEs

from the surfactant-rich phase also needs to be studied in detail.

38

Table 5. The recoveries (% ± sd, n=8) obtained for Pd, Pt, Rh and Ru and the matrix

elements (Al, Ce, Zr) with the CPE method applied to the catalyst sample solutions [II].

Sample Element Concentration range (mg L-1)a Recovery (%)

PGEs

SRM 2557 Pd 0.4–2 91 ± 6

SRM 2557 Pt 2–8 91 ± 5

SRM 2557 Rh 0.2–0.9 85 ± 6

Ru-catalyst Ru 9–40 66 ± 11

Matrix elements

SRM 2557 Al 200–640 4 ± 1

SRM 2557 Ce 23–89 4 ± 1

SRM 2557 Zr 0.2–0.3 2 ± 2

Ru catalyst Al 330–1200 4 ± 1

a 0.2, 0.4 and 0.8 g catalyst samples were leached with HCl at 120 °C.

4.2 PGEs in the environment

4.2.1 Elimination of spectral interferences in the determination of PGEs [III, IV]

Two different approaches to the elimination of spectral interferences in the

determination of PGEs in environmental samples (moss, road dust) were studied.

These analytical approaches included the combination of a chemical separation

method, CPE, with ICP-QMS determination and alternatively a direct instrumental

determination using ICP-MS/MS. The most abundant isotopes with no isobaric

interferences (101Ru, 103Rh, 105Pd, 193Ir, 195Pt and 197Au) were used in the

determinations with ICP-QMS after CPE. Several isotopes (if available) were

studied for Pd, Pt and Rh with ICP-MS/MS. Samples digested in a microwave oven

using aqua regia were analyzed. As the mass fractions of the PGEs in the

environmental samples were low, the sample pretreatment was kept as simple as

possible to avoid contamination.

CPE and ICP-QMS

The CPE procedure applying 2-MBT, Triton X-100 and SnCl2, based on papers by

Niemelä et al. for Pt [129] and Simitchiev et al. for Pd, Pt and Rh [128], was not

directly applicable to the studied samples due to the matrix containing aqua regia.

It was reported in both of these papers that samples with an oxidizing medium (e.g.,

39

aqua regia) are incompatible with the CPE method due to problems with the

oxidation states of the PGEs or oxidation of the complexing agent (2-MBT)

preventing complex formation. Similar problems have also been observed with

other CPE systems [103, 132]. Another explanation presented for low recoveries

obtained in the presence of nitric acid was an increase in the hydrophilic nature of

the PGE complexes [103].

The extraction efficiencies were studied in practice with PGE standard

solutions (10 µg L-1) containing HCl and/or HNO3. According to the results (Table

6), lower recoveries were observed when nitric acid was present in the solutions.

The behavior of Ru, Ir and Au, reported for the first time with this CPE method,

displayed similar trends to Pd, Pt and Rh. Au was extracted with better efficiency

than the other elements in solutions containing aqua regia, probably because of the

direct extraction of HAuCl4 to the surfactant-rich phase [133–135]. In spite of the

low recoveries obtained for the PGEs, the phase separation in the samples occurred

normally. This indicates that the problems were related to the complexation

processes.

Table 6. The recoveries (%, ±sd) obtained for PGEs and Au using the CPE method with

2-MBT, Triton X-100 and SnCl2 (n=3) [III].

Element Acid mixture component and concentration (mol L-1)

HCl (1.0) HCl (0.75) + HNO3 (0.31)a HCl (1.5) + HNO3 (0.64) HNO3 (1.0)

Ru 99 ± 2 48 ± 29 4 ± 1 3 ± 2

Rh 100 ± 2 71 ± 30 4 ± 1 5 ± 2

Pd 101 ± 3 72 ± 34 4 ± 1 7 ± 4

Ir 43 ± 7 27 ± 17 5 ± 1 4 ± 3

Pt 101 ± 3 84 ± 19 7 ± 1 17 ± 9

Au 96 ± 1 80 ± 12 65 ± 3 10 ± 8

a n=9, more than three replicates were prepared due to the high variation of the observed recoveries.

Based on the literature, two explanations for these observations were introduced.

On the one hand, S-nitrosation of the “active” thiol group (R-SH) in 2-MBT could

prevent the complexation with PGEs. This could happen due to nitrosyl chloride

(NOCl) formed in solutions containing aqua regia or due to the presence of nitrous

acid (HNO2 = HONO) in nitric acid solutions (Equation 1) [136]. The RSNOs

formed further decompose upon heating forming the corresponding disulfide and

NO (Equation 2). On the other hand, it is possible that nitrosyl complexes of PGEs

form (e.g., Ru(NO)Cl5) [137] and hinder the complexation with 2-MBT.

40

RSH + HNO2/NOCl RSNO + H2O/HCl (1) 2 RSNO ↔ RSSR + 2 NO (2)

Traditionally, the samples have been heated almost to dryness to remove any nitric

acid prior to the extraction of PGEs. This, however, is a time-consuming step and

the samples are prone to contamination. Thus, an approach of using sulfamic acid

to prevent the problems related to the presence of nitric acid was studied. It has

been previously stated that sulfamic acid is a compound able to displace NO+ ions

in Ru complexes [138]. In addition, sulfamic acid has been reported to act as a

scavenger of nitrous acid (Equation 3), thus preventing nitrosation reactions [139,

140].

NH2SO3H + HNO2 ↔ N2 + HSO4- + H2O + H+ (3)

Due to the changes made to the CPE method, the extraction conditions were

carefully optimized. The optimization was conducted stepwise (Table 7) starting

from preliminary parameters selected (mainly) according to Niemelä et al. [129].

Some compromises were made when selecting the optimal extraction conditions,

because not all of the elements always behaved in a similar way. For example, Pt

and Au actually showed contradictory behavior when the amount of Triton X-100

was optimized. In addition, low recoveries occasionally observed during the

method optimization posed a minor challenge. This behavior was assigned to the

use of MW-assisted heating, which has been previously reported to cause some

problems in power-controlled MW-assisted CPE [128]. Similar problems were not

observed when the experiments were conducted in a water bath. Thus, the

extraction in a water bath for 120 min was used as a reference and was observed to

yield similar recoveries to the MW-assisted CPE method.

Table 7. Optimization of the CPE method using 40 mL standard solutions (10 µg L-1

PGEs) with 0.75 mol L-1 HCl and 0.31 mol L-1 HNO3 [III].

Parameter Step Preliminary conditions Optimization range Selected conditions

Extraction time (min)a 1 60 30–90 75

10% Triton X-100 (mL) 2 2 1–5 3

Sulfamic acid (g) 2 0.5 0.3–0.7 0.5

1% 2-MBT (mL) 3 2 0.5–5 4

Temperature (°C) 4 95 90–95 90

a Extraction time in microwave oven. For extractions performed in water bath 120 min was used.

41

After optimizing the extraction method, the effect of different acid matrices (HCl

and/or HNO3, different dilutions) was studied. In aqua regia containing solutions

the recoveries were the highest in the lowest acid concentrations (Table 8). Very

good recoveries were obtained for Pd and Au in the two lowest acid concentrations.

The recoveries of Rh, Ru and Pt were slightly lower and the recovery of Ir was

clearly unsatisfactory. The recoveries of Pd, Pt, Rh, Ru and Au in the highest acid

concentration were still in the range of 74 to 94%. This is a great improvement

when compared to Table 6 (Pd, Pt, Rh and Ru from 4 to 7% and Au 65%). When

the results obtained in 1 mol L-1 HNO3 are compared, a significant increase in the

recoveries is obtained again. The method with SnCl2 outperformed the method with

sulfamic acid only in extraction of Pt, Rh and Ru in 1 mol L-1 HCl matrix. Probably

the use of SnCl2 offers better ligand exchange rates in those conditions.

Reliable analytical performance of the CPE method employing sulfamic acid

in the determination of Rh, Pd and Pt was confirmed by the good results obtained

for certified reference materials BCR-723 (road dust) and NIST SRM 2557 (used

automotive catalyst) (Table 9). Calibration standards were taken through the whole

sample preparation procedure to ensure that the acid concentration and speciation

of Pd, Pt and Rh were similar to the samples. Further, to study the effect of plant

matrix on the recoveries, Pd, Pt and Rh were determined also from uncontaminated

moss samples spiked with reference materials. The results were in good agreement

with the expected values. Furthermore, detection limits (3s, for a 500 mg sample)

of 0.89 µg kg-1 for Pd, 0.13 µg kg-1 for Pt and 0.19 µg kg-1 for Rh were calculated

using blank samples passed through the whole measurement protocol. These

detection limits were expected to be low enough for the analysis of slightly

contaminated moss samples.

Table 8. The recoveries (%, ±sd) of the PGEs and Au (n=3) obtained with different acids

and concentration levels using the optimized CPE method employing sulfamic acid [III].

Element Acid mixture component and concentration (mol L-1)

HCl (0.5) +

HNO3 (0.21)

HCl (0.75) +

HNO3 (0.31)a

HCl (1.0) +

HNO3 (0.41)

HCl (1.5) +

HNO3 (0.62)

HCl (1.0) HNO3 (1.0)

Ru 86 ± 4 82 ± 1 80 ± 5 78 ± 1 79 ± 1 87 ± 2

Rh 92 ± 5 89 ± 1 81 ± 3 83 ± 1 71 ± 2 94 ± 3

Pd 100 ± 3 99 ± 1 95 ± 2 94 ± 3 101 ± 1 100 ± 2

Ir 33 ± 7 23 ± 1 18 ± 3 17 ± 1 22 ± 3 37 ± 4

Pt 88 ± 5 81 ± 1 72 ± 4 74 ± 2 87 ± 1 82 ± 3

Au 99 ± 3 96 ± 1 92 ± 2 87 ± 3 99 ± 2 97 ± 1

a n=2

42

It must be noted, that interference elimination had a crucial role in the analysis

of BCR-723 as the results measured after MW digestion were clearly higher than

the certified values (Table 9). When the removal of elements possibly causing

interferences in the determinations of Pd, Pt and Rh was studied, approximately

99% of the studied elements (Cu, Hf, Pb, Sr, Y and Zn) were removed by using the

CPE procedure.

Table 9. Expected and determined (ICP-QMS) mass fractions for Pd, Pt and Rh in

reference materials (BCR-723 and SRM 2557) and in moss samples spiked with the

reference materials [III, IV].

Material Analyte Unit Expected Determined after

MW digestion

Determined after MW

digestion + CPE

BCR-723; 250 mg Pd µg kg-1 6.1 ± 1.9 277 ± 35 4.4 ± 1.0

n=9a Pt µg kg-1 81.3 ± 2.5 88 ± 10 73.4 ± 9.2

Rh µg kg-1 12.8 ± 1.3 31.1 ± 3.0 11.3 ± 1.5

BCR-723; 250 mg Pd µg kg-1 6.1 ± 1.9 - 6.3 ± 0.9

+ Moss; 250 mg Pt µg kg-1 81.3 ± 2.5 - 76 ± 10

n=3a Rh µg kg-1 12.8 ± 1.3 - 13.7 ± 1.9

SRM 2557; 5 mg Pd mg kg-1 233.2 ± 1.9 221 ± 3 207 ± 12

n=5b Pt mg kg-1 1131 ± 11 1081 ± 18 950 ± 67

Rh mg kg-1 135.1 ± 1.9 129 ± 2 123 ± 1

SRM 2557; 5 mg Pd mg kg-1 233.2 ± 1.9 - 209 ± 6

+ Moss; 500 mg Pt mg kg-1 1131 ± 11 - 1035 ± 43

n=3a Rh mg kg-1 135.1 ± 1.9 - 93 ± 16

a Sample digestion at 210 °C followed by CPE performed in water bath, b Sample digestion at 180 °C

followed by CPE performed in microwave oven.

ICP-MS/MS

In addition to the studied procedure combining CPE and ICP-QMS, the feasibility

of the ICP-MS/MS technique in the elimination of spectral interferences in the

determination of Pd, Pt and Rh in MW-digested samples was evaluated. Once again,

BCR-723 (road dust) was used to study the success of the interference elimination.

The “triple quadrupole” ICP-MS/MS instrument consists of two quadrupole

mass analyzers and an octopole-based collision/reaction cell located in between

them. Different gases or gas mixtures can be used in the collision/reaction cell for

interference elimination purposes. Alternatively, the instrument can be operated in

no gas mode. For Pd, the no gas mode and gas modes with He and NH3 (10% NH3

in He) to eliminate spectral interferences were studied. The results for the

43

determination of Pd in BCR-723 are presented in Table 10. When using the no gas

mode the Pd isotopes were suffering from severe spectral interferences. The

interferences were not removed with He, but ammonia showed potential for

interference elimination. Two different NH3 gas flow rates (2 and 3 mL min-1) were

studied and between these the higher flow rate appeared to be more efficient in

interference elimination. However, the monitored masses had to be carefully

selected. In general, the use of on-mass measurement with 105Pd+ (105→105),

originally suffering from oxide/hydroxide interferences, was more efficient than

the use of a mass-shift (105→156) corresponding to the formation of Pd(NH3)3+.

According to the results, significant unidentified interference(s) appeared in the

latter case. On the other hand, the on-mass measurements were not successful with 106Pd+ and 108Pd+ suffering from isobaric Cd interferences. This indicates that Cd is

not very reactive with ammonia. Even though 106Pd+ and 108Pd+ also suffer from

oxide/hydroxide interferences, the mass-shift measurements (106→157, 108→159)

were showing potential for Pd determination. Actually, the mass-shift of 108Pd+ to 108Pd(NH3)3

+ (i.e. 108→159) provided the closest result to the certified value for

BCR-723.

Table 10. Summary of Pd results in BCR-723 using different gas modes with ICP-MS/MS

(n=3) [IV]. The certified value for Pd is 6.1 ± 1.9 µg kg-1.

105Pd 106Pd 108Pd

m/z µg kg-1 m/z µg kg-1 m/z µg kg-1

No gasa on-mass 105 467 ± 13 106 340 ± 6 108 140 ± 2

He; 4 mL min-1 on-mass 105→105 594 ± 11 106→106 445 ± 4 108→108 183 ± 2

NH3b; 2 mL min-1 on-mass 105→105 28.1 ± 0.1 106→106 82.7 ± 1.2 108→108 58.8 ± 1.1

mass-shift 105→156 158 ± 5 106→157 38.5 ± 1.6 108→159 12.4 ± 2.4

NH3b; 3 mL min-1 on-mass 105→105 15.0 ± 1.0 106→106 73.7 ± 2.1 108→108 53.0 ± 1.6

mass-shift 105→156 110 ± 3 106→157 14.2 ± 1.0 108→159 6.2 ± 0.5

an=6, b10% NH3 in He

Spectral interferences were observed also in the determination of Rh in BCR-723.

The introduction of O2, He and NH3 to a collision/reaction cell reduced these

interferences. The best results were again obtained with NH3 (3 mL min-1), either

on-mass (103→103) or using a mass-shift corresponding to the formation of

Rh(NH3)4+ (103→171). Further, the results were consistent with the certified value.

The results obtained for Pt using its most abundant isotopes, 194Pt+ and 195Pt+, were

similar both using the no gas mode and a mass-shift to Pt(NH3)2+ with NH3 (3 mL

min-1). The isotopes 196Pt and 198Pt were originally suffering from isobaric Hg

44

interferences as well as from polyatomic oxide/hydroxide interferences. Also these

interferences were efficiently removed using mass-shifts (196→230, 198→232)

with NH3 (3 mL min-1).

Moss samples

The moss samples exposed to traffic-related emissions were expected to have

similar spectral interferences to those observed in BCR-723 (road dust). Both of

the interference elimination approaches, CPE with ICP-QMS and the ICP-MS/MS

technique, were used in the determinations of Pd, Pt and Rh mass fractions in these

samples. The ICP-MS/MS analyses were performed both in no gas mode and using

NH3 (3 mL min-1) for interference elimination. To ensure the comparability of the

results, the analyses were performed from the same MW-digested sample solutions.

The results for Pd are presented in Fig. 7. The results obtained using CPE with

ICP-QMS (105Pd) are plotted on the x-axis and the results obtained using ICP-

MS/MS (105Pd, 106Pd and 108Pd) on the y-axis. The results of the no gas mode are

presented on the left side of the figure and the results of the NH3 mode on the right

side of the figure. Despite a loss of sensitivity during the use of the NH3 mode with

ICP-MS/MS (4 to 13% of sensitivity left depending on the element and the type of

measurement) the detection limits were similar to the no gas mode. These

instrumental detection limits (3s, n=10, for a 500 mg sample) are presented in the

upper left corner of each plot.

It can be concluded, based on Fig. 7, that a direct determination of Pd was not

possible in the no gas mode. On the other hand, the interferences were efficiently

removed using an on-mass measurement with 105Pd+ (105→105) or a mass-shift

measurement with 108Pd+ (108→159). Interferences in the determination of 106Pd+

(106→157) were not fully eliminated, probably due to the presence of more severe

oxide/hydroxide interferences than with 108Pd+. These results are in good agreement

with those obtained for BCR-723, where the use of the mass-shift for 108Pd+

(108→159) was the recommended option. With Rh, both the on-mass measurement

(103→103) and the mass-shift measurement (103→171) gave similar results when

compared to those obtained with CPE and ICP-QMS. Therefore, both on-mass and

mass-shift measurements can be equally recommended for Rh analyses.

45

Fig. 7. The correlation of Pd mass fractions in moss samples determined by ICP-QMS

(105Pd) after CPE and by ICP-MS/MS using (A) no gas mode for 105Pd, (B) on-mass

measurement 105→105 with NH3 (3 mL min-1 of 10% NH3 in He) [IV], (C) no gas mode for 106Pd, (D) mass-shift measurement 106→157 with NH3 (3 mL min-1) [IV], (E) no gas mode

for 108Pd and (F) mass-shift measurement 108→159 with NH3 (3 mL min-1) [IV]. Detection

limits for ICP-MS/MS determination (3s) are presented in the upper left corner of the

figures.

y = 6,3944x + 23,596R² = 0,7717

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12

ICP

-MS

/MS

, no

gas

, 10

5 (µ

g kg

-1)

Cloud point extraction (µg kg-1)

Pd: ADL 0.22 µg kg-1

y = 0,9786x + 0,0965R² = 0,9772

0

2

4

6

8

10

12

0 2 4 6 8 10 12

ICP

-MS

/MS

, N

H3-

M,

105→

105

(µg

kg-1

)

Cloud point extraction (µg kg-1)

Pd: BDL 0.16 µg kg-1

y = 13,078x + 21,827R² = 0,8153

0

20

40

60

80

100

120

140

160

180

0 2 4 6 8 10 12

ICP

-MS

/MS

, no

gas

, 10

6 (µ

g kg

-1)

Cloud point extraction (µg kg-1)

Pd: CDL 0.23 µg kg-1

y = 1,1023x + 0,3201R² = 0,9647

0

2

4

6

8

10

12

0 2 4 6 8 10 12

ICP

-MS

/MS

, N

H3-

M,

106→

157

(µg

kg-1

)

Cloud point extraction (µg kg-1)

Pd: DDL 0.24 µg kg-1

y = 5,005x + 8,9947R² = 0,8583

0

10

20

30

40

50

60

70

0 2 4 6 8 10 12

ICP

-MS

/MS

, no

gas

, 10

8 (µ

g kg

-1)

Cloud point extraction (µg kg-1)

Pd: EDL 0.29 µg kg-1

y = 0,8446x + 0,2745R² = 0,9485

0

2

4

6

8

10

12

0 2 4 6 8 10 12

ICP

-MS

/MS

, N

H3-

M,

108→

159

(µg

kg-1

)

Cloud point extraction (µg kg-1)

Pd: FDL 0.23 µg kg-1

46

Furthermore, the determinations of 194Pt+ and 195Pt+ did not suffer from severe

spectral interferences, but the use of the mass-shifts (194→228, 195→229)

improved the precision of the results and yielded very good correlation with the

data obtained using CPE and ICP-QMS. Effective interference removal was

observed also using the mass-shifts (196→230, 198→232) with the Pt isotopes

suffering from more severe spectral interferences. For Pt, the use of 195Pt+ with a

mass-shift (195→229) appears to be the best option due to its highest natural

abundance and the lowest detection limit obtained.

Based on the results discussed above, the use of ICP-MS/MS is a simple and

reliable way to determine the low mass fractions of Pd, Pt and Rh in moss samples

collected for environmental monitoring. Furthermore, this technique is easy to

apply to large sample series, because the samples can be measured directly after

MW digestion.

4.2.2 Active biomonitoring of Pd, Pt and Rh with moss [V]

The analyzed moss samples were collected with the aim of evaluating the use of

Pleurozium schreberi, a terrestrial moss, for the active biomonitoring of traffic-

related Pd, Pt and Rh emissions. In addition, the samples were expected to give

information on current PGE emissions in Oulu, Finland. Moss mats were exposed

to emissions at three locations (Linnanmaa, Intiö and Hiironen) along highway E75

for 105 days. Additionally, five background samples were collected. Eighteen other

elements (Al, Ba, Cd, Ce, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Sr, V, Y, Zn and Zr)

were also determined using ICP-OES and ICP-QMS. These elements were used in

interpretation of the results as many of them are known to have a traffic-related

source.

The mass fractions (w, µg kg-1) for Pd, Pt and Rh in the moss samples,

determined using the ICP-MS/MS technique, are reported in Table 11. The results

are classified by the exposure site and the distance from the highway. Also

background values, based on samples collected from the original location of the

transplanted samples, are reported. In addition, relative accumulation factors (RAF,

Table 11) for PGEs (and other elements) were calculated using these background

values according to Equation 4.

RAF = (wexposed – wbackground) / wbackground (4)

For Pd, the detection limit was used as an estimate of wbackground. Based on the RAF

values, clearly elevated mass fractions of the PGEs were observed in the moss

47

samples, even at a distance of 12 m from the highway. When considering all the

studied elements, Pd, Pt and Rh were also among the most accumulated elements

[V]. When the mass fractions of Pd, Pt and Rh are considered, they are in a similar

range to those found in a previous passive biomonitoring study in Finland [62].

When compared to other active biomonitoring experiments, Auraylt et al. [66]

observed similar mass fractions for Pt (1.9-4.3 µg kg-1) and lower mass fractions

for Pd (0.7-2.5 µg kg-1) using samples at a distance of 2 m from a road in France.

On the other hand, Zechmeister et al. [65] observed clearly higher mass fractions

of Pd, Pt and Rh in a tunnel experiment (e.g., > 30 µg kg-1 Pt) in Austria.

Table 11. Mass fractions of Pd, Pt and Rh determined by ICP-MS/MS in µg kg-1 (average

± sd) in moss samples (background site n=5, other sites n=3 for each distance) [V]. Also,

average relative accumulation factors (RAF) are presented.

Exposure site Distance to

highway

Pd Pt Rh

µg kg-1 RAF µg kg-1 RAF µg kg-1 RAF

Background < 0.23b 0.4 ± 0.1 0.06 ± 0.03

Linnanmaa 2 m 2.4 ± 0.8 31.5 1.8 ± 0.8 4.0 0.55 ± 0.14 8.7

7 ma 1.8 ± 1.0 13.5 2.0 ± 1.6 4.6 0.52 ± 0.44 8.2

12 m 0.9 ± 0.5 8.6 0.7 ± 0.4 0.9 0.27 ± 0.13 3.7

Intiö 2 m 7.5 ± 1.2 9.5 6.6 ± 3.8 17.5 1.5 ± 0.8 25.4

7 m 3.3 ± 1.9 6.9 2.2 ± 1.9 5.1 0.37 ± 0.14 5.5

12 m 2.2 ± 0.6 2.7 0.8 ± 0.3 1.4 0.37 ± 0.13 5.5

Hiironen 2 m 3.1 ± 0.5 12.6 3.5 ± 3.0 8.9 0.61 ± 0.14 9.8

7 m 1.0 ± 0.7 3.2 0.9 ± 0.7 1.6 0.22 ± 0.15 2.8

12 m 1.2 ± 0.7 4.2 0.4 ± 0.3 0.1 0.12 ± 0.02 1.1

a n=2, b median < 0.23 (range < 0.23 - 0.53)

Some trends were observed when the results were studied more closely. The highest

mass fractions of Pd, Pt and Rh (and most of the other elements) were observed in

the Intiö site samples. This observation seems logical, because this exposure site

has the highest traffic density and it is located nearest to the city center of Oulu.

Also, a decreasing trend in the mass fractions of Pd, Pt and Rh was observed when

the distance to the highway increased. This trend was confirmed using statistical

treatment, i.e. the non-parametric Kruskal-Wallis test (p < 0.05). Actually, this trend

related to PGE emissions from road traffic is well-known [49, 50, 141], and thus

indicates that P. schreberi is well-suited for active biomonitoring experiments.

Also the correlations of Pd, Pt and Rh with each other and with the other

elements were studied. The Pearson’s correlation coefficients between the PGEs

were statistically significant and are presented with their corresponding scatter

48

plots in Fig. 8. The correlations between PGEs were somewhat lower than, for

example, between elements assigned to brake wear, Sb and Cu [142], presented for

comparison. A significant amount of the PGE emissions from catalytic converters

is expected to be in particulate form due to the abrasion of the catalyst materials

[143]. However, it must be noted that the composition of catalytic converters may

vary (e.g., by manufacturer, age or type of the converter). For example, Pt is much

more typical in catalytic converters of diesel vehicles when compared to Pd, due to

its resistance to oxidation or poisoning by sulfur species [144]. On the other hand,

Pd has replaced the more expensive Pt in many other catalytic converters. Thus, the

low amounts of PGEs together with the compositional differences in the catalytic

converters and an uneven distribution of the PGE-containing particles to the

roadside environment may explain this observation. Furthermore, strong

correlations between PGEs and other common traffic-related elements (e.g., Cu, Ni,

Sb, Zn, etc.) were observed [V].

Fig. 8. Scatter plots for Pt–Pd (a), Pt–Rh (b), Pd–Rh (c), and Sb–Cu (d) pairs presented

as white circles. The Pearson’s correlation coefficients for each pair are displayed on

the lower right corners of the figures. The background values are presented as black circles [V].

49

Elemental mass ratios are also commonly reported, when PGEs are determined in

environmental materials. The interpretation of these ratios is, however, not always

straightforward as many factors may have an effect on them. In addition to the

above-mentioned details also the mobility of the PGEs in the environment and the

contribution of additional emission sources in urban areas should be taken into

account [46, 95, 141]. As mosses retain elements both in particulate and soluble

forms, the moss samples collected next to the highway were considered to give a

reliable estimate of the current Pt/Pd, Pt/Rh and Pd/Rh ratios in Oulu, Finland. The

observed average ratios (n=26) were 0.80 for Pt/Pd, 4.1 for Pt/Rh and 5.8 for Pd/Rh.

The Pt/Rh ratio is comparable to a Pt/Rh ratio (average 3.9) obtained 10 years ago

in a passive biomonitoring study in Finland [62], whereas higher Pt/Rh ratios have

been observed, for example, in Austria [65]. There is no Finnish data available for

the other ratios. One must be careful if these ratios are compared to studies

conducted in other countries, possibly even many years ago. For example, when

the Pt/Pd ratio is considered, the ratios measured in other moss studies

approximately 10 years ago have, in general, been higher (range 0.9-12.5) than in

this study [59, 65, 66]. On the other hand, ratios < 1 are not exceptional when other

environmental materials are considered; for example, a ratio of 0.7 was reported in

tunnel dust samples in a recent study in Texas, USA [95].

Based on these observations, P. schreberi is well-suited for the active

biomonitoring of Pd, Pt and Rh emissions originating from road traffic. In the future,

P. schreberi could be used in tracking PGE emissions in urban or industrial areas.

In addition, valuable information about Pd, Pt and Rh emissions from Oulu, Finland

was collected in this study. This information can be used as a basis for regular

monitoring conducted in the Oulu area. Furthermore, due to the availability of the

ICP-MS/MS technique, environmental monitoring is becoming easier and could

cover also other elements such as Ru and Ir [50] in the future.

50

51

5 Conclusions

This thesis expands the knowledge of analytical methods related to the

determination of PGEs. Both high and low concentration levels were studied, with

the emphasis on the determination of Ru in catalyst materials and Pd, Pt and Rh in

environmental samples. The knowledge was also applied for studying the recovery

of Pd, Pt, Rh and Ru in catalyst materials and for monitoring the emissions of Pd,

Pt and Rh into the environment.

There was an evident need for a detailed study on the digestion methods for Ru

in catalyst samples, because Ru contents of the catalyst materials are often reported

as a part of catalyst development. In this study, acid digestions with HCl-HNO3

mixtures in a microwave oven or in an HPA were compared to sample digestion

using a fusion method. A good overview of the digestion efficiencies of these

methods was gained using Ru powder and the selected Ru compounds (RuO2·xH2O,

anhydrous RuO2 and RuCl3). These digestion methods were also applied for

alumina- and carbon-supported Ru catalysts. Whereas clear differences in the

digestion efficiencies of the studied compounds were observed, fusion being the

most efficient digestion method, the digestions of the catalyst materials displayed

similar results using all of the methods. Due to the different

advantages/disadvantages of the studied methods, it can be concluded that careful

consideration is needed when the digestion method for a particular set of catalysts

is selected.

In addition to Ru, also Pd, Pt and Rh are commonly available in (spent) catalyst

materials. In the recycling-related part of this study, the recovery of these metals

was studied using MW-assisted leaching and CPE. When compared to conductive

heating, the use of MW-heating speeded up the leaching processes. When several

temperatures and leach solutions (aqua regia, HCl and HNO3) were compared, it

was noticed that fast and efficient leaching of these metals from catalyst materials

was achieved using temperatures of 120 to 150 °C with aqua regia and HCl.

However, when the leaching temperature was increased, also the leaching of the

matrix elements increased. Further, the effect of L/S ratio on the leaching of Pd, Pt,

Rh and Ru was studied with ratios of 5 to 80 at 120 °C with HCl. In general, the

leaching was more efficient when higher ratios were used, but even the lower ratios

showed some potential. Additional factors, such as stirring during the heating stage

or longer leaching times should be considered in the future. However, the results

described here serve as a good basis for further studies and upscaling experiments.

52

CPE is a separation method used in analytical chemistry to pre-concentrate the

analytes and to separate them from interfering elements. This is done by extracting

hydrophobic complexes of PGEs to a small volume of surfactant-rich phase using

relatively environmentally friendly reagents (e.g., when compared to organic

solvents used in liquid-liquid extractions). Thus, CPE was expected to have

potential also in separating PGEs from the leach solutions or recovering PGEs from

dilute process waste solutions. For this purpose, a previously reported CPE method

was optimized for much higher PGE concentrations (< 0.2 µg L-1 to > 1 mg L-1)

and applied to diluted (1 M HCl) leach solutions. Recoveries around 90% for Pd,

Pt and Rh and around 66% for Ru were obtained, while 95% of the matrix elements

were removed.

CPE was used also for the elimination of interferences prior to the

determination of PGEs by ICP-QMS. The method was carefully optimized to

tolerate also the presence of nitric acid in the MW-digested sample solutions. For

this purpose, sulfamic acid was introduced to the method employing 2-MBT as a

complexing agent and Triton X-100 as a surfactant. Sulfamic acid was expected to

favor the complex formation processes and to prevent the decomposition of the

complexing agent by nitrous species present in the solutions. The analytical

performance of the method was confirmed using two certified reference materials,

SRM 2557 (used automotive catalyst) and BCR-723 (road dust). Furthermore, CPE

was used for determining the mass fractions of Pd, Pt and Rh in moss samples

exposed to traffic-related emissions.

The ICP-MS/MS technique, offering interesting opportunities for instrumental

elimination of spectral interferences, has recently been introduced to analytical

laboratories. Thus, the feasibility of this technique for the determination of Pd, Pt

and Rh in moss samples was studied. The validity of the developed method was

first studied using BCR-723 and the most successful interference elimination

conditions with NH3 (10% NH3 in He, 3 mL min-1) were applied for the moss

samples. Furthermore, the mass fractions determined for Pd, Pt and Rh in the moss

samples were compared to those obtained using CPE and ICP-QMS. An excellent

correlation between the results was found when 103Rh was determined on-mass

(103→103) or using a mass-shift corresponding to formation of Rh(NH3)4+

(103→171), 108Pd was determined with a mass-shift to Pd(NH3)3+ (108→159) and

195Pt was determined with a mass-shift to Pt(NH3)2+ (195→229). The use of ICP-

MS/MS technique significantly reduces the time required for the analyses since

only a complete digestion of PGEs is needed. As a consequence, this technique

holds great potential for future use.

53

The studied moss samples were originally collected with the aim of studying

the usefulness of Pleurozium schreberi (a terrestrial moss) for the active

biomonitoring of emissions of Pd, Pt and Rh from the road traffic in the Oulu region.

The mass fractions of Pd, Pt and Rh (ICP-MS/MS) and other traffic-related

elements (ICP-QMS or ICP-OES) were determined at three different distances

from, and at each of three different locations, along highway E75. These results

together with well-known trends and statistical treatment indicated that P. schreberi is well-suited for active biomonitoring experiments. In addition, valuable

information was gained to be compared to previous knowledge and to be used as a

basis for future monitoring campaigns. The availability of the ICP-MS/MS

technique also provides possibilities to expand the monitoring efforts both with the

number of samples collected and with the number of elements studied.

54

55

References

1. Rao CRM & Reddi GS. (2000) Platinum group metals (PGM); occurrence, use and recent trends in their determination. Trends Anal Chem 19: 565–586.

2. Gunn G. (2014) Platinum-group metals. In: Gunn G (ed) Critical metals handbook. Oxford, John Wiley & Sons: 284–311.

3. Cowley A. (2013) Platinum 2013 Interim review. Royston, Johnson Matthey PLC. 4. Deutschmann O, Knözinger H, Kochloefl K & Turek T. (2011) Heterogeneous catalysis

and solid catalysts, 3. Industrial applications. In: Ullmann's Encyclopedia of Industrial Chemistry, Weinheim, Wiley-VCH: 551–567.

5. Wheate NJ, Walker S, Craig GE & Oun R. (2010) The status of platinum anticancer drugs in the clinic and in clinical trials. Dalton Trans 39: 8113–8127.

6. Cabri LJ. (2002) The platinum-group minerals. In: Cabri LJ (ed) The geology, geochemistry, mineralogy and mineral beneficiation of platinum-group elements. Ottawa, Ontario, Canadian Institute of Mining, Metallurgy and Petroleum, Special Volume 54: 13–129.

7. Mudd GM. (2012) Key trends in the resource sustainability of platinum group elements. Ore Geol Rev 46: 106–117.

8. Gordon RB, Bertram M & Graedel TE. (2006) Metal stocks and sustainability. Proc Natl Acad Sci USA 103: 1209–1214.

9. Yang C-J. (2009) An impending platinum crisis and its implications for the future of the automobile. Energ Policy 37: 1805–1808.

10. Glaister BJ & Mudd GM. (2010) The environmental costs of platinum–PGM mining and sustainability: Is the glass half-full or half-empty? Minerals Eng 23: 438–450.

11. European Commission. (2010) Report on critical raw materials for the EU: Report of the ad hoc working group on defining critical raw materials.

12. European Commission. (2014) Report on critical raw materials for the EU: Report of the ad hoc working group on defining critical raw materials.

13. Hagelüken C. (2007) Closing the loop - Recycling of automotive catalysts. Metall 61: 24–39.

14. Hagelüken C. (2012) Recycling the platinum group metals: A European perspective. Platin Met Rev 56: 29–35.

15. Jha MK, Lee J-C, Kim M-S, Jeong J, Kim B-S & Kumar V. (2013) Hydrometallurgical recovery/recycling of platinum by the leaching of spent catalysts: A review. Hydrometallurgy 133: 23–32.

16. Kim C-H, Woo SI & Jeon SH. (2000) Recovery of platinum-group metals from recycled automotive catalytic converters by carbochlorination. Ind Eng Chem Res 39: 1185–1192.

17. Crundwell FK, Moats MS, Ramachandran V, Robinson TG & Davenport WG. (2011) Recycling of nickel, cobalt and platinum-group metals. In: Extractive metallurgy of nickel, cobalt and platinum group metals, Oxford, Elsevier Ltd: 537–549.

56

18. Benson M, Bennett CR, Harry JE, Patel MK & Cross M. (2000) The recovery mechanism of platinum group metals from catalytic converters in spent automotive exhaust systems. Resour Conserv Recycling 31: 1–7.

19. Willner J, Fornalczyk A, Cebulski J & Janiszewski K. (2014) Preliminary studies on simultaneous recovery of precious metals from different waste materials by pyrometallurgical method. Arch Metall Mater 59: 801–804.

20. Rumpold R & Antrekowitsch J. (2012) Recycling of platinum group metals from automotive catalysts by an acidic leaching process. Proceedings of the 5th International Platinum Conference, Sun City, South Africa, The Southern African Institute of Mining and Metallurgy: 695–713.

21. Baghalha M, Khosravian Gh. H & Mortaheb HR. (2009) Kinetics of platinum extraction from spent reforming catalysts in aqua-regia solutions. Hydrometallurgy 95: 247–253.

22. Barakat MA & Mahmoud MHH. (2004) Recovery of platinum from spent catalyst. Hydrometallurgy 72: 179–184.

23. Matjie RH, Scurrell MS & Bunt J. (2005) The selective dissolution of alumina, cobalt and platinum from a calcined spent catalyst using different lixiviants. Minerals Eng 18: 801–810.

24. Kizilaslan E, Aktaş S & Şeşen MK. (2009) Towards environmentally safe recovery of platinum from scrap automotive catalytic converters. Turk J Eng Environ Sci 33: 83–90.

25. Jimenez de Aberasturi D, Pinedo R, Ruiz de Larramendi I, Ruiz de Larramendi JI & Rojo T. (2011) Recovery by hydrometallurgical extraction of the platinum-group metals from car catalytic converters. Minerals Eng 24: 505–513.

26. Nogueira CA, Paiva AP, Oliveira PC, Costa MC & Rosa da Costa AM. (2014) Oxidative leaching process with cupric ion in hydrochloric acid media for recovery of Pd and Rh from spent catalytic converters. J Hazard Mater 278: 82–90.

27. Upadhyay AK, Lee J-C, Kim E-Y, Kim M-S, Kim B-S & Kumar V. (2013) Leaching of platinum group metals (PGMs) from spent automotive catalyst using electro-generated chlorine in HCl solution. J Chem Technol Biotechnol 88: 1991–1999.

28. Shams K, Beiggy MR & Gholamipour Shirazi A. (2004) Platinum recovery from a spent industrial dehydrogenation catalyst using cyanide leaching followed by ion exchange. Appl Catal A 258: 227–234.

29. Chen J & Huang K. (2006) A new technique for extraction of platinum group metals by pressure cyanidation. Hydrometallurgy 82: 164–171.

30. Zanjani A & Baghalha M. (2009) Factors affecting platinum extraction from used reforming catalysts in iodine solutions at temperatures up to 95° C. Hydrometallurgy 97: 119–125.

31. Patel A & Dawson R. (2015) Recovery of platinum group metal value via potassium iodide leaching. Hydrometallurgy 157: 219–225.

32. Jafarifar D, Daryanavard MR & Sheibani S. (2005) Ultra fast microwave-assisted leaching for recovery of platinum from spent catalyst. Hydrometallurgy 78: 166–171.

57

33. Niemelä M, Pitkäaho S, Ojala S, Keiski RL & Perämäki P. (2012) Microwave-assisted aqua regia digestion for determining platinum, palladium, rhodium and lead in catalyst materials. Microchem J 101: 75–79.

34. Gupta B & Singh I. (2013) Extraction and separation of platinum, palladium and rhodium using Cyanex 923 and their recovery from real samples. Hydrometallurgy 134–135: 11–18.

35. Lee JY, Raju B, Kumar BN, Kumar JR, Park HK & Reddy BR. (2010) Solvent extraction separation and recovery of palladium and platinum from chloride leach liquors of spent automobile catalyst. Sep Purif Technol 73: 213–218.

36. Marinho RS, Afonso JC & Dias da Cunha JWS. (2010) Recovery of platinum from spent catalysts by liquid–liquid extraction in chloride medium. J Hazard Mater 179: 488–494.

37. Mhaske AA & Dhadke PM. (2001) Extraction separation studies of Rh, Pt and Pd using Cyanex 921 in toluene—a possible application to recovery from spent catalysts. Hydrometallurgy 61: 143–150.

38. Nikoloski AN & Ang K-L. (2014) Review of the application of ion exchange resins for the recovery of platinum-group metals from hydrochloric acid solutions. Miner Process Extr Metal Rev 35: 369–389.

39. Nikoloski AN, Ang K-L & Li D. (2015) Recovery of platinum, palladium and rhodium from acidic chloride leach solution using ion exchange resins. Hydrometallurgy 152: 20–32.

40. Das N. (2010) Recovery of precious metals through biosorption—A review. Hydrometallurgy 103: 180–189.

41. Terrazas-Rodríguez JE, Gutiérrez-Granados S, Alatorre-Ordaz MA, Ponce de León C & Walsh FC. (2011) A comparison of the electrochemical recovery of palladium using a parallel flat plate flow-by reactor and a rotating cylinder electrode reactor. Electrochim Acta 56: 9357–9363.

42. Rauch S & Morrison GM. (2008) Environmental relevance of the platinum-group elements. Elements 4: 259–263.

43. Niskavaara H, Kontas E & Reimann C. (2004) Regional distribution and sources of Au, Pd and Pt in moss and O-, B-and C-horizon podzol samples in the European Arctic. Geochem Explor Env A 4: 143–159.

44. Van de Velde K, Barbante C, Cozzi G, Moret I, Bellomi T, Ferrari C & Boutron C. (2000) Changes in the occurrence of silver, gold, platinum, palladium and rhodium in Mont Blanc ice and snow since the 18th century. Atmos Environ 34: 3117–3127.

45. Barbante C, Veysseyre A, Ferrari C, Van De Velde K, Morel C, Capodaglio G, Cescon P, Scarponi G & Boutron C. (2001) Greenland snow evidence of large scale atmospheric contamination for platinum, palladium, and rhodium. Environ Sci Technol 35: 835–839.

46. Rauch S & Peucker-Ehrenbrink B. (2015) Sources of platinum group elements in the environment. In: Zereini F and Wiseman CLS (eds) Platinum metals in the environment. Berlin Heidelberg, Springer-Verlag: 3–17.

47. Zereini F & Wiseman CL (eds) (2015) Platinum metals in the environment. Berlin Heidelberg, Springer-Verlag.

58

48. Wichmann H, Anquandah GA, Schmidt C, Zachmann D & Bahadir MA. (2007) Increase of platinum group element concentrations in soils and airborne dust in an urban area in Germany. Sci Tot Environ 388: 121–127.

49. Zereini F, Wiseman C & Püttmann W. (2007) Changes in palladium, platinum, and rhodium concentrations, and their spatial distribution in soils along a major highway in Germany from 1994 to 2004. Environ Sci Technol 41: 451–456.

50. Fritsche J & Meisel T. (2004) Determination of anthropogenic input of Ru, Rh, Pd, Re, Os, Ir and Pt in soils along Austrian motorways by isotope dilution ICP-MS. Sci Tot Environ 325: 145–154.

51. Ek KH, Morrison GM & Rauch S. (2004) Environmental routes for platinum group elements to biological materials—a review. Sci Tot Environ 334–335: 21–38.

52. Harmens H, Norris DA, Steinnes E, Kubin E, Piispanen J, Alber R, Aleksiayenak Y, Blum O, Coşkun M, Dam M, De Temmerman L, Fernández JA, Frolova M, Frontasyeva M, González-Miqueo L, Grodzińska K, Jeran Z, Korzekwa S, Krmar M, Kvietkus K, Leblond S, Liiv S, Magnússon SH, Maňkovská B, Pesch R, Rühling Å, Santamaria JM, Schröder W, Spiric Z, Suchara I, Thöni L, Urumov V, Yurukova L & Zechmeister HG. (2010) Mosses as biomonitors of atmospheric heavy metal deposition: Spatial patterns and temporal trends in Europe. Environ Pollut 158: 3144–3156.

53. Harmens H, Norris DA, Sharps K, Mills G, Alber R, Aleksiayenak Y, Blum O, Cucu-Man S-M, Dam M, De Temmerman L, Ene A, Fernández JA, Martinez-Abaigar J, Frontasyeva M, Godzik B, Jeran Z, Lazo P, Leblond S, Liiv S, Magnússon SH, Maňkovská B, Pihl Karlsson G, Piispanen J, Poikolainen J, Santamaria JM, Skudnik M, Spiric Z, Stafilov T, Steinnes E, Stihi C, Suchara I, Thöni L, Todoran R, Yurukova L & Zechmeister HG. (2015) Heavy metal and nitrogen concentrations in mosses are declining across Europe whilst some “hotspots” remain in 2010. Environ Pollut 200: 93–104.

54. Ares A, Aboal JR, Carballeira A, Giordano S, Adamo P & Fernández JA. (2012) Moss bag biomonitoring: a methodological review. Sci Tot Environ 432: 143–158.

55. Fernández JA, Aboal JR & Carballeira A. (2000) Use of native and transplanted mosses as complementary techniques for biomonitoring mercury around an industrial facility. Sci Tot Environ 256: 151–161.

56. Ares Á, Fernández JÁ, Aboal JR & Carballeira A. (2011) Study of the air quality in industrial areas of Santa Cruz de Tenerife (Spain) by active biomonitoring with Pseudoscleropodium purum. Ecotoxicol Environ Saf 74: 533–541.

57. Calabrese S, D’Alessandro W, Bellomo S, Brusca L, Martin RS, Saiano F & Parello F. (2015) Characterization of the Etna volcanic emissions through an active biomonitoring technique (moss-bags): Part 1 – Major and trace element composition. Chemosphere 119: 1447–1455.

58. Deljanin I, Antanasijević D, Vuković G, Urošević MA, Tomašević M, Perić-Grujić A & Ristić M. (2015) Lead spatio-temporal pattern identification in urban microenvironments using moss bags and the Kohonen self-organizing maps. Atmos Environ 117: 180–186.

59

59. Djingova R, Kovacheva P, Wagner G & Markert B. (2003) Distribution of platinum group elements and other traffic related elements among different plants along some highways in Germany. Sci Tot Environ 308: 235–246.

60. Niemelä M, Perämäki P, Piispanen J & Poikolainen J. (2004) Determination of platinum and rhodium in dust and plant samples using microwave-assisted sample digestion and ICP-MS. Anal Chim Acta 521: 137–142.

61. Cyprien M, Barbaste M & Masson P. (2008) Comparison of open digestion methods and selection of internal standards for the determination of Rh, Pd and Pt in plant samples by ICP-MS. Int J Environ Anal Chem 88: 525–537.

62. Niemelä M, Piispanen J, Poikolainen J & Perämäki P. (2007) Preliminary study of the use of terrestrial moss (Pleurozium schreberi) for biomonitoring traffic-related Pt and Rh deposition. Arch Environ Contam Toxicol 52: 347–354.

63. Beccaloni E, Coccia AM, Musmeci L, Stacul E & Ziemacki G. (2005) Chemical and microbial characterization of indigenous topsoil and mosses in green urban areas of Rome. Microchem J 79: 271–289.

64. Reimann C, Arnoldussen A, Boyd R, Finne TE, Nordgulen Ø, Volden T & Englmaier P. (2006) The influence of a city on element contents of a terrestrial moss (Hylocomium splendens). Sci Tot Environ 369: 419–432.

65. Zechmeister HG, Hagendorfer H, Hohenwallner D, Hanus-Illnar A & Riss A. (2006) Analyses of platinum group elements in mosses as indicators of road traffic emissions in Austria. Atmos Environ 40: 7720–7732.

66. Ayrault S, Li C & Gaudry A. (2006) Biomonitoring of Pt and Pd with mosses. In: Zereini F and Alt F (eds) Palladium Emissions in the Environment. Berlin Heidelberg, Springer-Verlag: 525–536.

67. Zechmeister HG, Hann S & Koellensperger G. (2015) Monitoring of platinum group element deposition by bryophytes. In: Zereini F and Wiseman CLS (eds) Platinum metals in the environment. Berlin Heidelberg, Springer-Verlag: 339–349.

68. Balcerzak M, Święcicka E & Balukiewicz E. (1999) Determination of platinum and ruthenium in Pt and Pt–Ru catalysts with carbon support by direct and derivative spectrophotometry. Talanta 48: 39–47.

69. Balcerzak M, Święcicka E & Bystrońska D. (1999) Simple selective spectrophotometric method for the determination of ruthenium in carbon supported Pt-Ru-Ge catalyst. Anal Lett 32: 1799–1805.

70. Taddia M & Sternini P. (2001) Improvements in the sample preparation for the determination of ruthenium in catalysts by different spectrometric techniques. Ann Chim 91: 239–244.

71. Fabec JL. (1983) Determination of ruthenium on impregnated or ion-exchanged oxide supports by flame atomic absorption spectrometry. At Spectrosc 4: 46–48.

72. Scaccia S & Goszczynska B. (2004) Sequential determination of platinum, ruthenium, and molybdenum in carbon-supported Pt, PtRu, and PtMo catalysts by atomic absorption spectrometry. Talanta 63: 791–796.

60

73. Fabec JL & Ruschak ML. (1983) Determination of aluminum, cobalt, lanthanum, and ruthenium on alumina-based catalysts by inductively coupled plasma atomic emission spectrometry. Anal Chem 55: 2241–2246.

74. Balcerzak M. (2002) Analytical methods for the determination of ruthenium: the state of the art. Crit Rev Anal Chem 32: 181–226.

75. Bencs L, Ravindra K & Van Grieken R. (2003) Methods for the determination of platinum group elements originating from the abrasion of automotive catalytic converters. Spectrochim Acta B 58: 1723–1755.

76. Balcerzak M. (2011) Methods for the determination of platinum group elements in environmental and biological materials: a review. Crit Rev Anal Chem 41: 214–235.

77. Balcerzak M. (2002) Sample digestion methods for the determination of traces of precious metals by spectrometric techniques. Anal Sci 18: 737–750.

78. Godlewska-Żyłkiewicz B. (2004) Preconcentration and separation procedures for the spectrochemical determination of platinum and palladium. Microchim Acta 147: 189–210.

79. Sato T. (1989) Volatilization behaviour of ruthenium from boiling nitric acid. J Radioanal Nucl Chem 129: 77–84.

80. Sato T. (1990) Volatilization behaviour of ruthenium from boiling solutions. J Radioanal Nucl Chem 139: 25–29.

81. Rauch S, Motelica-Heino M, Morrison GM & Donard OFX. (2000) Critical assessment of platinum group element determination in road and urban river sediments using ultrasonic nebulisation and high resolution ICP-MS. J Anal At Spectrom 15: 329–334.

82. Moldovan M, Krupp EM, Holliday AE & Donard OFX. (2004) High resolution sector field ICP-MS and multicollector ICP-MS as tools for trace metal speciation in environmental studies: a review. J Anal At Spectrom 19: 815–822.

83. Prohaska T. (2015) Interferences. In: Prohaska T, Irrgeher J, Zitek A and Jakubowski N (eds) Sector field mass spectrometry for elemental and isotopic analysis. Cambridge, The Royal Society of Chemistry: 121–125.

84. Djingova R, Heidenreich H, Kovacheva P & Markert B. (2003) On the determination of platinum group elements in environmental materials by inductively coupled plasma mass spectrometry and microwave digestion. Anal Chim Acta 489: 245–251.

85. Rodríguez-Castrillón JÁ, Moldovan M & García Alonso JI. (2009) Internal correction of hafnium oxide spectral interferences and mass bias in the determination of platinum in environmental samples using isotope dilution analysis. Anal Bioanal Chem 394: 351–362.

86. Gomez MB, Gomez MM & Palacios MA. (2000) Control of interferences in the determination of Pt, Pd and Rh in airborne particulate matter by inductively coupled plasma mass spectrometry. Anal Chim Acta 404: 285–294.

87. Rauch S, Lu M & Morrison GM. (2001) Heterogeneity of platinum group metals in airborne particles. Environ Sci Technol 35: 595–599.

61

88. Simitchiev K, Stefanova V, Kmetov V, Andreev G, Sanchez A & Canals A. (2008) Investigation of ICP-MS spectral interferences in the determination of Rh, Pd and Pt in road dust: Assessment of correction algorithms via uncertainty budget analysis and interference alleviation by preliminary acid leaching. Talanta 77: 889–896.

89. Müller M & Heumann KG. (2000) Isotope dilution inductively coupled plasma quadrupole mass spectrometry in connection with a chromatographic separation for ultra trace determinations of platinum group elements (Pt, Pd, Ru, Ir) in environmental samples. Fresenius J Anal Chem 368: 109–115.

90. Whiteley JD & Murray F. (2003) Anthropogenic platinum group element (Pt, Pd and Rh) concentrations in road dusts and roadside soils from Perth, Western Australia. Sci Tot Environ 317: 121–135.

91. Rudolph E, Limbeck A & Hann S. (2006) Novel matrix separation—on-line pre-concentration procedure for accurate quantification of palladium in environmental samples by isotope dilution inductively coupled plasma sector field mass spectrometry. J Anal At Spectrom 21: 1287–1293.

92. Leśniewska BA, Godlewska-Żyłkiewicz B, Ruszczyńska A, Bulska E & Hulanicki A. (2006) Elimination of interferences in determination of platinum and palladium in environmental samples by inductively coupled plasma mass spectrometry. Anal Chim Acta 564: 236–242.

93. Sutherland RA, Pearson DG & Ottley CJ. (2007) Platinum-group elements (Ir, Pd, Pt and Rh) in road-deposited sediments in two urban watersheds, Hawaii. Appl Geochem 22: 1485–1501.

94. Qi L, Zhou M-F, Zhao Z, Hu J & Huang Y. (2011) The characteristics of automobile catalyst-derived platinum group elements in road dusts and roadside soils: a case study in the Pearl River Delta region, South China. Environ Earth Sci 64: 1683–1692.

95. Spada N, Bozlaker A & Chellam S. (2012) Multi-elemental characterization of tunnel and road dusts in Houston, Texas using dynamic reaction cell-quadrupole-inductively coupled plasma–mass spectrometry: Evidence for the release of platinum group and anthropogenic metals from motor vehicles. Anal Chim Acta 735: 1–8.

96. Zhao P, Li J, Zhong L, Sun S & Xu J. (2014) A method for determination of PGE–Re concentrations and Os isotopic compositions in environmental materials. Anal Methods 6: 5537–5545.

97. Meisel T, Fellner N & Moser J. (2003) A simple procedure for the determination of platinum group elements and rhenium (Ru, Rh, Pd, Re, Os, Ir and Pt) using ID-ICP-MS with an inexpensive on-line matrix separation in geological and environmental materials. J Anal At Spectrom 18: 720–726.

98. Bruzzoniti MC, Cavalli S, Mangia A, Mucchino C, Sarzanini C & Tarasco E. (2003) Ion chromatography with inductively coupled plasma mass spectrometry, a powerful analytical tool for complex matrices: Estimation of Pt and Pd in environmental samples. J Chromatogr A 997: 51–63.

99. Pearson DG & Woodland SJ. (2000) Solvent extraction/anion exchange separation and determination of PGEs (Os, Ir, Pt, Pd, Ru) and Re–Os isotopes in geological samples by isotope dilution ICP-MS. Chem Geol 165: 87–107.

62

100. Gomez MB, Gomez MM & Palacios MA. (2003) ICP-MS determination of Pt, Pd and Rh in airborne and road dust after tellurium coprecipitation. J Anal At Spectrom 18: 80–83.

101. Leśniewska BA, Godlewska-Żyłkiewicz B, Bocca B, Caimi S, Caroli S & Hulanicki A. (2004) Platinum, palladium and rhodium content in road dust, tunnel dust and common grass in Białystok area (Poland): a pilot study. Sci Tot Environ 321: 93–104.

102. Alsenz H, Zereini F, Wiseman CLS & Püttmann W. (2009) Analysis of palladium concentrations in airborne particulate matter with reductive co-precipitation, He collision gas, and ID-ICP-Q-MS. Anal Bioanal Chem 395: 1919–1927.

103. Meeravali NN & Jiang S-J. (2008) Interference free ultra trace determination of Pt, Pd and Au in geological and environmental samples by inductively coupled plasma quadrupole mass spectrometry after a cloud point extraction. J Anal At Spectrom 23: 854–860.

104. Meeravali NN, Kumar SJ & Jiang S-J. (2010) An acid induced mixed-micelle mediated cloud point extraction for the separation and pre-concentration of platinum from road dust and determination by inductively coupled plasma mass spectrometry. Anal Methods 2: 1101–1105.

105. Stalikas CD. (2002) Micelle-mediated extraction as a tool for separation and preconcentration in metal analysis. Trends Anal Chem 21: 343–355.

106. Paleologos EK, Giokas DL & Karayannis MI. (2005) Micelle-mediated separation and cloud-point extraction. Trends Anal Chem 24: 426–436.

107. Bezerra MA, Arruda MAZ & Ferreira SLC. (2005) Cloud point extraction as a procedure of separation and pre‐concentration for metal determination using spectroanalytical techniques: A review. Appl Spectrosc Rev 40: 269–299.

108. Ojeda CB & Rojas FS. (2009) Separation and preconcentration by a cloud point extraction procedure for determination of metals: an overview. Anal Bioanal Chem 394: 759–782.

109. Ojeda CB & Rojas FS. (2012) Separation and preconcentration by cloud point extraction procedures for determination of ions: recent trends and applications. Microchim Acta 177: 1–21.

110. Köllensperger G, Hann S & Stingeder G. (2000) Determination of Rh, Pd and Pt in environmental silica containing matrices: capabilities and limitations of ICP-SFMS. J Anal At Spectrom 15: 1553–1557.

111. Fragnière C, Haldimann M, Eastgate A & Krähenbühl U. (2005) A direct ultratrace determination of platinum in environmental, food and biological samples by ICP-SFMS using a desolvation system. J Anal At Spectrom 20: 626–630.

112. Simpson LA, Thomsen M, Alloway BJ & Parker A. (2001) A dynamic reaction cell (DRC) solution to oxide-based interferences in inductively coupled plasma mass spectrometry (ICP-MS) analysis of the noble metals. J Anal At Spectrom 16: 1375–1380.

113. Kan SF & Tanner PA. (2004) Determination of platinum in roadside dust samples by dynamic reaction cell-inductively coupled plasma-mass spectrometry. J Anal At Spectrom 19: 639–643.

63

114. Ohno T, Muramatsu Y, Shikamori Y, Toyama C, Okabe N & Matsuzaki H. (2013) Determination of ultratrace 129I in soil samples by Triple Quadrupole ICP-MS and its application to Fukushima soil samples. J Anal At Spectrom 28: 1283–1287.

115. Bolea-Fernandez E, Balcaen L, Resano M & Vanhaecke F. (2015) Interference-free determination of ultra-trace concentrations of arsenic and selenium using methyl fluoride as a reaction gas in ICP–MS/MS. Anal Bioanal Chem 407: 919–929.

116. Balcaen L, Woods G, Resano M & Vanhaecke F. (2013) Accurate determination of S in organic matrices using isotope dilution ICP-MS/MS. J Anal At Spectrom 28: 33–39.

117. Amais RS, Amaral CDB, Fialho LL, Schiavo D & Nóbrega JA. (2014) Determination of P, S and Si in biodiesel, diesel and lubricating oil using ICP-MS/MS. Anal Methods 6: 4516–4520.

118. Balcaen L, Bolea-Fernandez E, Resano M & Vanhaecke F. (2014) Accurate determination of ultra-trace levels of Ti in blood serum using ICP-MS/MS. Anal Chim Acta 809: 1–8.

119. Bishop DP, Hare DJ, Fryer F, Taudte RV, Cardoso BR, Cole N & Doble PA. (2015) Determination of selenium in serum in the presence of gadolinium with ICP-QQQ-MS. Analyst 140: 2842–2846.

120. Jackson BP, Liba A & Nelson J. (2015) Advantages of reaction cell ICP-MS on doubly charged interferences for arsenic and selenium analysis in foods. J Anal At Spectrom 30: 1179–1183.

121. Bokhari SNH, Meisel T & Walkner C. (2015) Interference removals on Palladium and Gold with ICP-QQQ-MS in platinum group elements reference materials. European Winter Conference on Plasma Spectrochemistry, 22.–26.2.2015, Münster, Germany: FU2-PO11, available from: http://www.ewcps2015.org/program/show.html?aid=288& pid=278&bck=/program/day-2/session-POSTER [9.11.2015].

122. Bokhari SNH, Meisel T, Walkner C, Braga R & Funari V. (2015) Determination of Rh, Ir and Ag in Platinum Group Elements (PGE) reference materials (RM) for industrial analytics. ANAKON 2015 Book of Abstracts, 23.–26.3.2015, Graz, Austria: 259.

123. Bokhari SNH, Meisel T & Walkner C. (2015) Interference removals on Pd, Ru and Au with ICP-QQQ-MS in PGE RM. EGU General Assembly Conference Abstracts, vol. 17, 12.–17.4.2015, Vienna, Austria: Abstract id 13473, available from: http://adsabs.harvard.edu/abs/2015EGUGA..1713473N [9.11.2015].

124. Bokhari SNH, Meisel T & Walkner C. (2015) Removal of interferences on platinum in platinum group elements (PGE) reference materials (RM). The 9th international conference on the analysis of geological and environmental materials, 9.–14.8.2015, Leoben, Austria: 56.

125. Sugiyama N & Shikamori Y. (2015) Removal of spectral interferences on noble metal elements using MS/MS reaction cell mode of a triple quadrupole ICP-MS. J Anal At Spectrom 30: 2481–2487.

126. Balcaen L, Bolea-Fernandez E, Resano M & Vanhaecke F. (2015) Inductively coupled plasma – Tandem mass spectrometry (ICP-MS/MS): A powerful and universal tool for the interference-free determination of (ultra)trace elements – A tutorial review. Anal Chim Acta 894: 7–19.

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127. Steinnes E, Rühling Å, Lippo H & Mäkinen A. (1997) Reference materials for large-scale metal deposition surveys. Accred Qual Assur 2: 243–249.

128. Simitchiev K, Stefanova V, Kmetov V, Andreev G, Kovachev N & Canals A. (2008) Microwave-assisted cloud point extraction of Rh, Pd and Pt with 2-mercaptobenzothiazole as preconcentration procedure prior to ICP-MS analysis of pharmaceutical products. J Anal At Spectrom 23: 717–726.

129. Niemelä M, Huttunen SM, Gornostayev SS & Perämäki P. (2009) Determination of Pt from coke samples by ICP-MS after microwave assisted digestion and microwave assisted cloud point extraction. Microchim Acta 166: 255–260.

130. Foelske A, Barbieri O, Hahn M & Kötz R. (2006) An X-ray photoelectron spectroscopy study of hydrous ruthenium oxide powders with various water contents for supercapacitors. Electrochem Solid-State Lett 9: A268–A272.

131. Al-Harahsheh M, Kingman S & Bradshaw S. (2006) The reality of non-thermal effects in microwave assisted leaching systems? Hydrometallurgy 84: 1–13.

132. Mesquita da Silva MA, Frescura VLA & Curtius AJ. (2001) Determination of noble metals in biological samples by electrothermal vaporization inductively coupled plasma mass spectrometry, following cloud point extraction. Spectrochim Acta B 56: 1941–1949.

133. Akita S, Rovira M, Sastre AM & Takeuchi H. (1998) Cloud-point extraction of gold(lll) with nonionic surfactant—Fundamental studies and application to gold recovery from printed substrate. Sep Sci Technol 33: 2159–2177.

134. Chen S & Zhu X. (2010) Simplified cloud point extraction-inductively coupled plasma mass spectrometry for the preconcentration/analysis of ultra-trace gold. Minerals Eng 23: 1152–1154.

135. Manzoori JL, Abdolmohammad-Zadeh H & Amjadi M. (2007) Simplified cloud point extraction for the preconcentration of ultra-trace amounts of gold prior to determination by electrothermal atomic absorption spectrometry. Microchim Acta 159: 71–78.

136. Williams DLH. (1999) The Chemistry of S-Nitrosothiols. Acc Chem Res 32: 869–876. 137. Cleare MJ. (1968) Nitrosyl complexes of the platinum metals. Platin Met Rev 12: 131–

133. 138. Fitoussi R, Lours S & Musikas C. (1981) Commissariat a l'Energie Atomique, assignee.

Ruthenium Recovery Process by Solvent Extraction, US Patent 4.282.112. 139. Fitzpatrick J, Meyer TA, O'Neill ME & Williams DLH. (1984) Comparison of the

reactivity of nine nitrous acid scavengers. J Chem Soc, Perkin Trans 2: 927–932. 140. Williams DLH. (2004) Nitrosation reactions and the chemistry of nitric oxide.

Amsterdam, Elsevier B.V. 141. Ely JC, Neal CR, Kulpa CF, Schneegurt MA, Seidler JA & Jain JC. (2001) Implications

of platinum-group element accumulation along U.S. roads from catalytic-converter attrition. Environ Sci Technol 35: 3816–3822.

142. Dongarrà G, Manno E & Varrica D. (2009) Possible markers of traffic-related emissions. Environ Monit Assess 154: 117–125.

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143. Moldovan M, Palacios MA, Gómez MM, Morrison G, Rauch S, McLeod C, Ma R, Caroli S, Alimonti A, Petrucci F, Bocca B, Schramel P, Zischka M, Pettersson C, Wass U, Luna M, Saenz JC & Santamaría J. (2002) Environmental risk of particulate and soluble platinum group elements released from gasoline and diesel engine catalytic converters. Sci Tot Environ 296: 199–208.

144. Jollie D. (2009) Platinum 2009. Royston, Johnson Matthey PLC.

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Original publications

I Suoranta T, Niemelä M & Perämäki P (2014) Comparison of digestion methods for the determination of ruthenium in catalyst materials. Talanta 119: 425–429.

II Suoranta T, Zugazua O, Niemelä M & Perämäki P (2015) Recovery of palladium, platinum, rhodium and ruthenium from catalyst materials using microwave-assisted leaching and cloud point extraction. Hydrometallurgy 154: 56–62.

III Suoranta T, Niemelä M & Perämäki P (2014) Cloud point extraction of platinum group elements and gold: elimination of nitric acid-related problems with sulphamic acid. Anal Methods 6: 9321–9327 (http://pubs.rsc.org/en/content/articlelanding/2014/ ay/c4ay02264e).

IV Suoranta T, Bokhari SNH, Meisel T, Niemelä M & Perämäki P (2016) Elimination of interferences in the determination of palladium, platinum and rhodium mass fractions in moss samples using ICP-MS/MS. Geostand Geoanal Res DOI 10.1111/ggr.12116.

V Suoranta T, Niemelä M, Poikolainen J, Piispanen J, Bokhari SNH, Meisel T & Perämäki P (2016) Active biomonitoring of palladium, platinum, and rhodium emissions from road traffic using transplanted moss. Environ Sci Pollut Res DOI 10.1007/s11356-016-6880-1.

Reprinted with permission from Elsevier (I, II), The Royal Society of Chemistry

(III), John Wiley and Sons (IV) and Springer (V).

Original publications are not included in the electronic version of the dissertation.

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665. Varanka, Sanna (2016) Multiscale influence of environmental factors on waterquality in boreal rivers : application of spatial-based statistical modelling

666. Luukkonen, Tero (2016) New adsorption and oxidation-based approaches forwater and wastewater treatment : studies regarding organic peracids, boiler-water treatment, and geopolymers

667. Tolkkinen, Mari (2016) Multi-stressor effects in boreal streams : disentangling theroles of natural and land use disturbance to stream communities

668. Kaakinen, Juhani (2016) Öljyllä ja raskasmetalleilla pilaantuneita maita koskevanympäristölainsäädännön ja lupamenettelyn edistäminen kemiallisella tutkimuksella

669. Huttunen, Kaisa-Leena (2016) Biodiversity through time : coherence, stability andspecies turnover in boreal stream communities

670. Rönkä, Nelli (2016) Phylogeography and conservation genetics of waders

671. Fucci, Davide (2016) The role of process conformance and developers' skills inthe context of test-driven development

672. Manninen, Outi (2016) The resilience of understorey vegetation and soil toincreasing nitrogen and disturbances in boreal forests and the subarcticecosystem

673. Pentinsaari, Mikko (2016) Utility of DNA barcodes in identification anddelimitation of beetle species, with insights into COI protein structure across theanimal kingdom

674. Lassila, Toni (2016) In vitro methods in the study of reactive drug metaboliteswith liquid chromatography / mass spectrometry

675. Koskimäki, Janne (2016) The interaction between the intracellular endophyticbacterium, Methylobacterium extorquens DSM13060, and Scots pine (Pinussylvestris L.)

676. Ronkainen, Katri (2016) Polyandry, multiple mating and sexual conflict in a waterstrider, Aquarius paludum

677. Pulkkinen, Elina (2016) Chemical modification of single-walled carbon Nanotubesvia alkali metal reduction

678. Runtti, Hanna (2016) Utilisation of industrial by-products in water treatment :Carbon-and silicate-based materials as adsorbents for metals and sulphateremoval

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ADVANCED ANALYTICAL METHODS FOR PLATINUM GROUP ELEMENTSAPPLICATIONS IN THE RESEARCH OF CATALYST MATERIALS, RECYCLING AND ENVIRONMENTAL ISSUES

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