INTRODUCTION

Coal fly ash is known for its enriched metal contents but was studied mostly in the field of pollution monitoring and

influences on the ecological system [1]. Our goal is to examine the possible recycling potential by determining the

contents of target elements, usually metals like Au, Pt or U, which are present in trace concentration levels. Due to its

harsh matrix properties, fly ash analysis is a challenging topic, usually demanding intensive sample pre-treatment.

Typically some kind of digestion step is involved to separate the organic matrix. These approaches are labor and time

demanding and propose the risk of sample-contamination during pre-treatment, furthermore sample dilution

accomplished during sample digestion hampers sensitive measurement of target analytes.

BCR® - 176 R from

EC-JRC-IRMM and

was applied to fly ash

samples originating

from the Vienna

community heating

combustion plant.

In this work, an ETV-based method for direct, fast and accurate ICP-MS-analysis of trace elements and noble

metals is proposed. Sample preparation is reduced to simple dispersion of the particulate sample in diluted nitric acid.

An aliquot of the derived slurry solution is transferred to a graphite-boat and introduced to an electro thermal

vaporization unit coupled to an ICP-MS. The developed method was validated using certified reference material.

MS Parameters

ICP-MS measurements were carried

out on a Thermo iCAP ICP-MS.

Analyte masses were chosen

according to their abundance,

possible interferences and to the

quality of their respective calibration

curve (Co59, Ni60, Cd111, In115,

Pt195, Au197, Tl205, U238).

EXPERIMENTAL

Analytical procedure

• the fly ash samples were dispersed (concentration < 1 mg/10 ml) in 1% (v/v) nitric acid and engaged in a slurry state by means of a vortexer and ultrasonic agitation

• 20 µl of slurry solution were transferred into a graphite boat and the solvent was slowly evaporated by means of an IR-Lamp

• the graphite boat was planted into the ETV-4000 graphite furnace (Spectral Systems, Germany) an a temperature program (see Figure I) was applied.

•Analytes were transferred from ETV 4000 to ICP-MS and emission signals were recorded in transient signal mode (intensity vs. time).

G.Bauer*, A Limbeck*

* Vienna University of Technology, Institute of Chemical Technologies and Analytics, Getreidemarkt 9/164-IAC, 1060 Vienna, Austria

ACCURATE ANALYSIS OF TRACE METALS IN FLY ASH

USING ELECTRO-THERMAL–VAPORISATION

IN COMBINATION WITH ICP-MS DETECTION

Figure I: optimized temperature program

0

500

1000

1500

2000

2500

0 20 40 60 80 100

tem

per

atu

re [

°C]

time [s]

Table I:

instrument parameters

RF power [W] 1200

plasma gas flow rate [L/min] 13

nebulizer flow rate [L/min] 0.52*

auxiliary flow rate [L/min] 0.8

Freon modifier [mL/min] 10

*sum of carrier gas and cooling gas

SAMPLES

The samples originated from the Vienna community heating combustion plant:

sample 1: FLA – fly ash

sample 2: KSA – sludge ash

sample 3: Schlacke – bed ash

Table II:

correlation between ICP-MS analysis

and SRM certified values

[mg/kg] Co

SRM certified concentration 26.7

± 1.6

Results ICP-MS analysis 27.0

± 1.0

METHOD VALIDATION

Standard reference material SRM BCR

176R was used

• to evaluate the signal quantification

and

• to test the accuracy of the method

OUTLOOK

Quantification of Gold and Uranium

Validation of ETV-ICP-MS analysis with

REE CRM

Expanding the number of analytes

REFERENCES

[1] Michaela Kröppl, Irene Lahoz Muñoz, Michaela Zeiner,

Toxicological & Environmental Chemistry, 93:5, 886-894 (2011)

[2] M. Resano, F. Vanhaecke and M. T. C. de Loos-Vollebregt, J. Anal.

At. Spectrom., 23, 1450–1475 (2008)

sample dispersion

IR-pre-drying

Temperature program

Atomization and ionization

Mass filter

Transient signal detection

iCAP Q (Thermo Scientific)

ETV 4000 (Spectral Systems)

Figure II: Transient signals and peak shapes in ETV-ICP-MS, Pt (green), U (pink) and Au (blue)

RESULTS

The presence of Uranium was confirmed for the all samples. Comparing the sample

results against each other the following relation was found:

KSA:FLA:Schlacke = 100:20:65

Small amounts of Gold are found in all samples but are still at or below LOD

(see Table II). Results for Co and Pt are displayed in Table III.

Table II ETV-ICP-MS

RSDs (n = 4): 3 %

[ng/boat] Au Co Pt

LOD (3 σ) 0.090 0.036 0.70

LOQ (10 σ) 0.099 0.043 0.82

Table III ETV-ICP-MS

RSDs (n = 3): < 10 %

[mg/kg] Au Co Pt

KSA < LOD 236 ± 18 32.7 ± 1.0

FLA 40.7 ± 0.4 319 ± 28 37.6 ± 1.0

Schlacke < LOD 409 ± 40 41.5 ± 3.9