Research Article Solar UV-Assisted Pretreatment of …downloads.hindawi.com/journals/ac/2014/938419.pdfResearch Article Solar UV-Assisted Pretreatment of River Water Samples for the

Research ArticleSolar UV-Assisted Pretreatment of River Water Samples forthe Voltammetric Monitoring of Nickel and Cobalt Ultratraces

Gelaneh Woldemichael1 and Gerd-Uwe Flechsig234

1 School of Natural Science Adama Science and Technology University Adama Ethiopia2 School of Science and the Environment Manchester Metropolitan University Manchester M1 5GD UK3Gensoric GmbH Schillingallee 68 18057 Rostock Germany4Department of Chemistry University of Rostock 18059 Rostock Germany

Correspondence should be addressed to Gerd-Uwe Flechsig gflechsigmmuacuk

Received 29 April 2014 Revised 17 June 2014 Accepted 17 June 2014 Published 21 July 2014

Academic Editor Mohamed Sarakha

Copyright copy 2014 G Woldemichael and G-U Flechsig This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

The application of solar UV radiation as sample digestion method is reported The method is employed in adsorptive strippingvoltammetric determination of nickel and cobalt in river water samples The river water samples were collected from downstreamof Warnow River (Germany) and acidified to pH of 2 plusmn 02 by addition of ultrapure 65 HNO

3 Furthermore 34mgLminus1 ultrapure

hydrogen peroxide solution was added to the samples as photochemical reaction initiator The samples were transferred to UV-Atransparent polyethylene terephthalate bottles and put in the sunshine for UV irradiation for six and 12 hours at a UV-A intensityof 390mWm2 The comparison of the concentration values showed that 6 hours of solar UV irradiation at 390mWm2 UV-Aintensity is not sufficient to complete the digestion process though it yields much better results than the undigested original sampleHowever 12 hours of solar UV-A irradiation under similar conditions is almost as effective as a 30W artificial UV lamp (254 nm)and can be applied to the digestion of dissolved organic carbon in trace nickel (II) and cobalt (II) analysis in natural waters such asriver water lake waters and well waters

1 Introduction

The determination of trace metals in natural waters likeriver water is crucial especially for those metals causinghealth hazards and environmental effects Metal pollutantsexist bounded by organic andor inorganic matrices in theenvironment and thus the determination of these metals innatural waters becomes complicated unless they are separatedfrom the matrices by application of proper sample pre-treatment methods [1] Electrochemical methods and espe-cially the voltammetric determination of metal ions requirehomogenous samples free of organic matter which interactswith themetal ions andwith the electrodematerial Dissolvedorganic matter (DOM) may form complexes with metal ionspreventing them from reduction at the working electrode orshifting the electrochemical redox potential towards negativedirection Such compounds can also affect the determination

by interacting with the electrode material forming adsorbedfilms or changing surface tension Furthermore DOM canundergo electrochemical redox reactions at the electrodesleading to increased background currents Thus DOM canmake the voltammetric determination of trace metals impos-sible [2]

Methods like wet digestion and dry ashing have beenemployed formany decades However thesemethods involvehigh risk of contamination [3] that comes from impuri-ties of the oxidizing agents like mineral acids bisulfatesor others These methods also require ultrapure reagentswhich is relatively unaffordable by many laboratories espe-cially in developing countries Clean efficient and envi-ronmentally friendly methods like UV digestions are alsoin use since their introduction by Armstrong et al in1966 [4] UV radiation decomposition has been describedfor DDT (11(441015840-dichlorodiphenyl)-222-trichloroethane)

Hindawi Publishing CorporationAdvances in ChemistryVolume 2014 Article ID 938419 7 pageshttpdxdoiorg1011552014938419

2 Advances in Chemistry

HCB (hexachlorobenzene) PCP (pentachlorophenol) TNT(135-trinitrotoluene) [5] and atrazine (a herbicide) [6]following absorption of 180ndash250 nm radiation

Under the influence of UV radiation different oxidantslike singlet oxygen [7] superoxide radicals and alkylperoxyradicals [8] and hydroxyl radical and hydrogen peroxide[9] are formed The subsequent reaction of these radicalswith organic matter is one of the natural ways of biodegra-dation in aquatic systems [9ndash12] Microwave-assisted high-temperature UV digestion procedure was developed for theaccelerated decomposition of interfering dissolved organiccarbon (DOC) prior to trace element analysis of liquid sam-ples such as industrialmunicipal wastewater groundwatersurface water body fluids infusions beverages and sewage[13] UV digestion instruments for theUVphotolysis of watersamples with a low to moderate amount of organic matterwere developed and commercially available for use Howeverthese instruments are relatively expensive which makes themdifficult to be used in some laboratories

Solar UV radiation was used in the presence of semi-conductors as catalysts in photodegradation of phenol [1415] We recently reported on a direct solar UV digestionmethod for stripping-voltammetric determination of zinccadmium lead and copper Only small amounts of oxidant(H2O2) were necessary for the pre-treatment of natural water

samples (riverwater) that contained lowDOCconcentrations[16] The addition of H

2O2to the samples before irradiation

increased the mineralization efficiency of the H2O2UV

system (88 of total organic carbon (TOC) reduction)compared with a UV-Only system (28 TOC reduction)at 4 hours of irradiation [16] Also uranium ultratracescould be detected this way [17] Therefore the applicationof solar radiation as a UV source for sample preparationhelps the application to be effective in many laboratoriesbecause of its natureThemethod is cheap clean mobile andenvironmentally friendly

Being essential elements cobalt and nickel become toxicat higher concentration because of their interaction withbiological systems [18] Nickel for instance needs exhaustiveecochemical and ecotoxicological investigations on its fateand behavior in ecosystem of terrestrial and aquatic envi-ronment It is among the toxic metals a significant topicof environmental surveillance food control occupationalmedicine toxicology and hygiene [19] Adsorptive strippingvoltammetry (AdSV) for cobalt and nickel elements was animportant advancement permitting lower detection limits[20] This involves a nonelectrolytic preconcentration step[21] In this case [20] the accumulation of Co and Ni asdimethylglyoxime (DMG) complexes in ammoniacal bufferat the hanging mercury drop electrode (HMDE) is followedby reduction of the adsorbed complex to the zero oxidationstate

In this paper both nickel (II) and cobalt (II) are deter-mined in river water samples by differential pulse adsorptivestripping voltammetric (DP-AdSV)method after the sampleswere digested by means of solar UV (UV-A) radiationin presence of hydrogen peroxide The effects of differentUV treatment protocols are also investigated by means ofpseudopolarography

Table 1 Instrumental parameters for AdSV experiments

Working electrode SMDEMeasurement mode DPPurging time 600 sPulse amplitude 005VDeposition potential minus07 VDeposition time 120 sEquilibration time 5 sStart potential minus08VEnd potential minus12 VVoltage step 0005VVoltage step time 03 sSweep rate 0013Vs

2 Experimental

21 Instrumentation A 120583Autolab potentiostat (Ecochemie)with General Purpose Electrochemical System (GPES) 49software package was connected to a Metrohm 663 VA Standwith an electrolysis cell equipped with a three-electrodesystemThe latter consisted of a HMDE as working electrodea glassy carbon counter electrode and a AgAgCl (3M KCl)reference electrode and was used for both the calibrationstudies and the pseudopolarographic experiments Differ-ential Pulse Adsorptive Stripping Voltammetric (DP-AdSV)method was used in both cases with the parameters given inTable 1

22 Reagents Ultrapure water (gt182MΩcmminus1 TOC lt2 120583gLminus1) was produced using an Ultra Clear system by SGWater GmbH Germany (now Evoqua Water TechnologiesLLC httpwwwwatersiemenscom) in order to prepareall solutions All reagents were obtained from certified man-ufacturers (Fluka Merck) and were delivered as analyticalgrade or ultrapure grade reagents (TraceSelect or Suprapur)where possible NH

3NH4Cl buffer (pH = 95) was prepared

as supporting electrolyte from ammonia solution (119908NH3 =25) and hydrochloric acid (119908HCl = 30) 01molLminus1 ofdimethylglyoxime (DMG) in ethanol and triethanolamine(TEA) in water (1 1) were prepared as complexing agentsin AdSVmeasurements Commercial 1000mgLminus1 stock solu-tions of the metals (Ni2+ and Co2+) were diluted as requiredfor standard additions 65 HNO

3was used to acidify the

water samples to pH 2 plusmn 02 (1mLLminus1) and 30 H2O2

was added to speed up the UV photocatalytic degradationprocess After the UV irradiation periods 10 120583L of 01molLminus1hydroxylammonium sulfate was added to 20mL of eachsample to remove newly formed nitrite and hypochlorite aswell as any remaining H

2O2

23 Sample Collection Preparation and Preservation Riverwater samples were collected in July 2011 based on the riverwater sampling protocols (EPA guidelines for regulatorymonitoring and testing water and waste water)The sampling

Advances in Chemistry 3

Table 2 Experimental result for nickel (II) in 0 hours irradiated (Original Sample) 6 and 12 hours solar UV irradiated (SoUV Sample) and6 hours artificial UV irradiated (UV Sample)

NickelOriginal Sample SoUV Sample UV Sample

0 hrs 6 hrs 12 hrs 6 hrsConcentration (120583gLminus1) 166 plusmn 006 212 plusmn 010 262 plusmn 006 271 plusmn 002

Recovery rate () 8780 plusmn 095 9080 plusmn 055 9520 plusmn 043 9900 plusmn 042

Blank recovery rate () 10048 plusmn 020

site was located at the south bank of Unterwarnow (the estu-ary ofWarnow River in Rostock Germany at 54∘051015840381210158401015840N12∘091015840063310158401015840E) Laboratory grade PEplastic bottleswere usedas sample containers after careful cleaningThe samples wereacidified with ultrapure HNO

3to adjust the pH to 2 plusmn 02

After taking the sample to the laboratory it was filteredthrough a 045 120583mpore size cellulose acetate membrane filterinserted in a Millipore filtration glass assembly and then34mgLminus1 H

2O2was added Then the same sample was

divided into three aliquots in containers labeled as OriginalSample 6-hour SoUV Sample 12-hour SoUV Sample andUV Sample We stored the Original Sample in a refrigeratorat 4∘C until determination The two SoUV Samples weretransferred to a carefully cleaned UV-A transparent (330ndash450 nm) polyethylene terephthalate (PET) bottle and exposedto solar radiation of UV-A intensity of ca 36mWcmminus2 for 6and 12 hours respectively We transferred the third aliquotdesignated as UV Sample to a UV-transparent (200ndash450 nm)quartz glass tube and irradiated for 6 hours by means of a30W artificial UV source generating a 254 nm UV radia-tion (low-pressure mercury-vapor lamp) The blank sampleswere obtained by performing the same sample pretreatmentprocedures from acidification with nitric acid to irradiationthough using ultrapure water instead of river water

The solar irradiation period was chosen to be inmidsum-mer (July 2011) between 1000 am and 400 pm to obtainmaximum efficiency of solar radiation as a result of increaseof latitude and the incident angle of the radiation fromthe sun In addition to this an aluminum solar collectorwas used to increase the solar radiation intensity This alsoincreased the infrared intensity of the incident radiationenhancing the synergetic effect of elevated water temperatureand UV radiation [18] All the three samples were stored in arefrigerator at 4∘C until determination Artificial river watercontaining 1000mgLminus1 humic acid was prepared to compareand estimate the concentration of humic acid in the originalWarnowRiver water bymeans ofUVVis spectrophotometryHumic acid is the most abundant component of dissolvedorganic water in natural waters such as river water

24 Procedure For each analysis 20mL of the river watersamples was taken into the voltammetric cell To this cell1 mL of ammonia buffer was added as a supporting electrolyteand to adjust the pH of the solution to 95 Similarly150 120583L of 010molLminus1 of DMG in ethanol and 15000120583L oftriethanolamine (TEA) in a 1 1 water solutionwere added as acomplexing agent After deaeration by purging with nitrogen

for 600 s the two heavy metals were analyzed simultaneouslyunder the given operating conditions and three replicatemeasurements were taken for each of the four categories ofsample specified in sample preparation procedure Standardaddition method was used to determine the concentrationsof the metal ions in the samples Pseudopolarographic datafor nickel were taken by DP-AdSV with a HMDE as workingelectrode and a supporting electrolyte of NH

3NH4Cl (pH of

95)Also here three replicate measurements were performed

for each metal of the four sample categories To estimatethe concentration of humic acid in the original river watersample UVVis spectra were recorded for Original Sampletwofold diluted Original Sample 6-hour and 12-hour SoUVSamples and UV Samples Afterwards these spectra werecompared with those of an artificial river water samplecontaining 1000 mgLminus1 humic acid

3 Results and Discussion

31 Standard Addition Experiments and Recovery RatesFigure 1 displays DP-AdSV responses of river water samplespretreated in different ways All the data are based upon stan-dard addition experiments The analytical results obtainedby extrapolation of the standard addition calibration curves(Figures 2 and 3) are given in Table 2

Nickel concentrations determined in the river waterincreased by 28 and 58 upon irradiation with solar UVfor 6 and 12 hours respectively Irradiation with artificial UVlight for 6 hours led to a 63 increase in the detected nickelconcentration

The Original Sample would not show any significantincrease of cobalt (II) peak current even after the additionof 3 120583gLminus1 of cobalt (II) standard solution This revealsthat DOM in the river water complexed all of the addedcobalt (II) ions For the 6- and 12-hour SoUV Samplesthere were no significant increases in the cobalt (II) peakcurrent after the addition of 2 120583gLminus1 of cobalt (II) Thisindicates that complexing organic matter was still presentin the water consuming up to 2 120583gLminus1 cobalt (II) thus thedigestion process was incomplete For the UV Sample thepeak current increase was significantly improved suggestingthe completion of the digestion process Here a standardaddition calculation was conducted using quadratic fit Ingeneral 12 hours of solar UV irradiation was not enough tocomplete the digestion at the given solar UV intensity Thisis why we observed deviation of the cobalt (II) calibration


Table 3 Experimental results for cobalt (II) in the 0 hours irradiated (Original Sample) 6 and 12 hours solar UV irradiated (SoUV Sample)and 6 hours artificial UV irradiated (UV Sample)

CobaltControl SoUV UV0hrs 6 hrs 12 hrs 6 hrs

Concentration (120583gLminus1) 000 000 000 033 plusmn 002



Table 4 Determination of the recovery rate for nickel (II) in 0 hours irradiated (Original Sample) 6 and 12 hours solar UV irradiated (SoUVSample) and 6 hours artificial UV irradiated (UV Sample)

Nickel Concentration beforespiking (120583gLminus1)

Spiked concentration(120583gLminus1)

Concentration afterspiking (120583gLminus1)

Recoveredconcentration (120583gLminus1) Recovery rate ()

Original Sample 166 500 605 439 87806 h SoUV Sample 212 500 666 454 908012 h SoUV Sample 262 500 738 476 9520UV Sample 271 500 766 495 9900Blank 000 500 502 502 10048

curve from linearity The results also indicate that cobalt (II)could be used for titration of complexing compounds in riverwater We used square functions for regression fits and tocalculate the concentration of cobalt (II) for the UV SampleThe calculated cobalt (II) concentration in the UV Samplewas 033 120583gLminus1 (Table 3) These findings indicate that morethan 12 hours of solar UV irradiation is needed to completethe digestion in Central Europe or otherwise more intensesolar UV radiation (such as equatorial or tropical sun) wouldbe needed for cobalt determination Furthermore the effectsof UV irradiation were confirmed by improvements of therecovery rate (Tables 4 and 5)

We did not calculate the concentration of cobalt (II) in theOriginal Samples and the 6- and 12-hour SoUV Samples usingcalibration curves because of the substantial deviation fromlinearity Instead we calculated the percentage of DOM thathad been decomposed by solar and artificial UV irradiationfrom the recovery experiments The determination of recov-ery values for nickel was conducted using standard additionmethod by spiking concentrations of 5 10 and 15120583gLminus1 ofnickel (II) following an addition of 5 120583gLminus1 nickel (II) inthe very beginning right before sample pretreatment to berecovered as a known concentration value in all types ofsamples

In the case of cobalt (II) we spiked 8120583gLminus1 of the metalions to theOriginal Sample inwhich only 360120583gLminus1 (4500)was recovered and thus 440 120583gLminus1 (55) was complexed bynatural matrix components The standard additions in thiscase were 8 and 16 120583gLminus1 of cobalt (II) standard solutionThe known concentration of cobalt (II) spiked to the othersamples was 2 120583gLminus1 Therefore the added standard concen-trations were 2 and 4 120583gLminus1 of cobalt (II) standard solutionWe used linear calibration plots in these standard additionsto calculate the recovered amount of cobalt (II) The resultsof the recovery tests clearly showed the presence of too muchDOM in theOriginal Sample (enough to complex 440 120583gLminus1

of added cobalt (II)) in the river water sample In the caseof the 6- and 12-hour SoUV Samples and the UV Samplesonly 059 048 and 027 120583gLminus1 were absorbed indicating theequivalent concentration of undigested complexing ligandsThus we observed that only 1341 1090 and 614 percent ofthe original DOM were remaining after 6- and 12-hour solarand artificial UV irradiation respectively In other words8659 8910 and 9386 percent of the original complexingligands were destroyed after 6-hour solar UV 12-hour solarUV and artificial UV irradiation respectively

Both metals can be complexed with either ligands fromthe river water (eg humic acids) or the DMG used as theAdSV agent in our stripping voltammetric experiments Bothsorts of ligands are competing for the metal ions in thesample and a major fraction is usually bound by the naturalmatrix ligands making it unavailable for stripping analysisTherefore the natural matrix ligands have to be destroyedfirst and this can be done by UV digestion Our resultsdemonstrate that even irradiation with UV-A from sunlightcan remove major parts of the natural matrix ligands Ofcourse longer irradiation time is expected to complete UVdigestion However this is not easy to achieve in CentralEurope Therefore we recommend this sample pretreatmentprocedure for regions of low geographic latitude which wehave already tested at low latitude equatorial region

32 Pseudopolarography Figure 4 depicts pseudopolaro-grams of nickel (II) recorded in Warnow River water sam-ples without any pretreatment (Original Sample) and afterthe various irradiation procedures (SoUV Sample and UVSample) The cobalt (II) level in these samples was too lowto be detected in all irradiation experiments The resultsdemonstrate a dramatic effect of the UV irradiation upon thestripping response of nickel (II) in the range between 105and 0V potential depositions Whereas the maximal achiev-able voltammetric signals increased 10-fold for artificial UV


Table 5 Determination of the recovery rate for cobalt (II) in 0 hours irradiated (Original Sample) 6 and 12 hours solar UV irradiated (SoUVSample) and 6 hours artificial UV irradiated (UV Sample)

Cobalt Concentration beforespiking (ppb)

Spiked concentration(ppb)

Concentration afterspiking (ppb)

Recoveredconcentration (ppb) Recovery rate ()

Original 000 800 360 360 45006 hrs SoUV 000 200 130 130 650012 hrs SoUV 000 200 145 145 7250UV 033 200 206 173 8650Blank 000 200 205 205 10234

Ni

0

minus30

minus60

minus90

minus12 minus11 minus10 minus09 minus08

EVS AgAgCl (V)

I(n

A)

(a)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(b)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(c)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(d)

Figure 1 Voltammograms of nickel (II) and cobalt (II) for (a) Original Sample (b) 6-hour SoUV Sample (c) 12-hour SoUV Sample and (d)UV Samplemeasured in the presence of ammonia buffer (NH

3NH4Cl pH = 95) as a supporting electrolyte and DMG-TEA as complexing

agents The standard concentrations were 5 10 and 15 120583gLminus1 for nickel (II) and 1 2 and 3 120583gLminus1 for cobalt (II)

and 7-fold for solar UV irradiation also the potentials shiftedtowards positive direction Both the pseudopolarographicldquohalf waverdquo potential and the current maximum potentialwere shifted bymax 300mVThismeans that with increasingUV irradiation dose it becomes easier to form and adsorb

the [Ni(dmgH)2] complex during the accumulation step in

AdSV measurementsThe effects of solar UV irradiation treatment were larger

in case of nickel (II) and cobalt (II) compared with our earlierstudies of zinc cadmium lead and copper [15] The main


5 10 15 200

0

50

100

(a)

(b)

(c)

(d)

I(n

A)

c (120583gLminus1)

Figure 2 Standard addition calibration curves for nickel (II) in (a)Original Sample (b) 6-hour SoUVSample (c) 12-hour SoUVSampleand (d) 6-hourUVSample Added standard concentrations of nickelwere 5 10 and 15 120583gLminus1

0

0

10

20

30

40

1 2 3 4 5 6

(a)

(b)

(c)

I(n

A)

c (ppb)

Figure 3 Standard addition calibration curves for Co (II) in (a) 6-hour SoUV (b) 12-hour SoUV Sample and (c) 6-hour UV SampleAdded concentrations of Co were 2 4 and 6 ppb

reason can be found in complexation of the analyte cationswhich is on one hand needed for adsorptive accumulationOn the other hand this desired process competes withcomplexation of the metal ions and humic substance ligandsThe latter interactions seem to be strong as well Anotherreason can be found in interfacial activity of the dissolvedorganic compounds in river water samples as they disturb theadsorptive accumulation of the analyte ion complexes withDMG

33 UV-Vis Spectrophotometry UV-Vis spectral absorptionof the samples was observed at 300 nm which is a char-acteristic band of excitation of 120587-electrons in the benzenering which is also the major structural constituent of humicsubstances like humic acid and fulvic acid The peak heights

0

minus10

minus20

minus12 minus08 minus04 00

(a)

(b)

(c)

(d)

I pea

k(n

A)

Edep (V)

Figure 4 AdSV pseudopolarograms of nickel for Original Sample(a) 6-hour SoUV Sample (b) 12-hour SoUV Sample (c) and 6-hour UV Sample (d) The single stripping voltammograms wererecorded within a potential range from minus02V to minus12 V in thepresence of NH

3NH4Cl buffer at pH 95 as supporting electrolyte

and DMG-TEA as complexing agents while other instrumentaloperating parameters were kept constant as given in Table 1

250 300 350

(a)(b)(c)

(d)(e)

(f)

(g)

04

03

02

01

00

Abso

rban

ce

Wavelength (nm)

Figure 5 UV-Vis spectra for (a) blank (b) 6-hour UV Sample (c)12-hour SoUV Sample (d) 6-hour SoUV Sample (e) 10 ppm humicacid (f) 2-fold diluted Original Sample and (g) Original Sample

suggest that the concentration of this humic substance inthe artificial UV irradiated sample is less than 100mgLminus1while that of 6-hour solar UV irradiated sample is nearly100mgLminus1 The spectral pattern suggests that the amount ofdissolved organic matter (DOM) decreased with intensifiedUV irradiation (Figure 5) That means an increasing radia-tion dose results in the decomposition and removal of thedissolved UV-absorbing organic matter In a similar mannerwe have estimated the concentration of humic substance inthe original river water sample to be 10-fold of 100mgLminus1humic acid that is about 100mgLminus1 Humic substances are


also the most important component of DOM in the riverwater at that concentration

4 Conclusions

We found that hydrogen peroxide-assisted irradiation of riverwater samples with solar UV provides effective means forsample preparation as needed for AdSV determination ofnickel and cobalt on hanging mercury drop electrodes Theeffect of UV irradiation treatment was even larger comparedto anodic stripping voltammetry of 4 other heavymetals (ZnCd Pb and Cu) in the same river as reported earlier

The approach reported here should be very useful formobile electrochemical heavymetal analysis in regionswhereintense sunlight is available

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors are grateful to the German Research Foundation(DFG FL 3847-1 Heisenberg Fellowship) and the GermanAcademic Exchange Service (DAAD) for financial support

References

[1] E P Achterberg C B Braungardt R C Sandford and P JWorsfold ldquoUV digestion of seawater samples prior to thedetermination of copper using flow injection with chemilumi-nescence detectionrdquo Analytica Chimica Acta vol 440 no 1 pp27ndash36 2001

[2] J Golimowski andK Golimowska ldquoUV-photooxidation as pre-treatment step in inorganic analysis of environmental samplesrdquoAnalytica Chimica Acta vol 325 no 3 pp 111ndash133 1996

[3] Z Filipovic-Kovacevic and L Sipos ldquoVoltammetric determina-tion of copper in water samples digested by ozonerdquo Talanta vol45 no 5 pp 843ndash850 1998

[4] F A J Armstrong P M Williams and J D H StricklandldquoPhoto-oxidation of organic matter in sea water by ultra-violetradiation analytical and other applicationsrdquoNature vol 211 no5048 pp 481ndash483 1966

[5] H S Son S J Lee I H Cho and K D Zoh ldquoKineticsand mechanism of TNT degradation in TiO

2photocatalysisrdquo

Chemosphere vol 57 no 4 pp 309ndash317 2004[6] T Viehweg and W Thiemann ldquoDie photochemische Elimina-

tion von Atrazin und seinen Metaboliten in WasserprobenrdquoVomWasser vol 79 pp 355ndash362 1992

[7] P B Merkel and D R Kearns ldquoRadiationless decay of singletmolecular oxygen in solution Experimental and theoreticalstudy of electronic-to-vibrational energy transferrdquo Journal of theAmerican Chemical Society vol 94 no 21 pp 7244ndash7253 1972

[8] R M Baxter and J H Carey ldquoEvidence for photochemicalgeneration of superoxide ion in humic watersrdquoNature vol 306no 5943 pp 575ndash576 1983

[9] X Zhou and K Mopper ldquoDetermination of photochemicallyproduced hydroxyl radicals in seawater and freshwaterrdquoMarineChemistry vol 30 pp 71ndash88 1990

[10] T Mill D G Hendry and H Richardson ldquoFree-radical oxi-dants in natural watersrdquo Science vol 207 no 4433 pp 886ndash8871980

[11] W R Haag and J Hoigne ldquoPhoto-sensitized oxidation innatural water via OH radicalsrdquo Chemosphere vol 14 no 11-12pp 1659ndash1671 1985

[12] D Kotzias H Parlar and F Korte ldquoPhotoreactivity of organicchemicals in water in the presence of nitrate and nitriterdquoNaturwissenschaften vol 69 no 9 pp 444ndash445 1982

[13] O C Zafiriou J Joussot-Dubien R G Zepp and R G ZikaldquoPhotochemistry of natural watersrdquo Environmental Science andTechnoalogy vol 18 no 12 pp 358Andash371A 1984

[14] D Florian and G Knapp ldquoHigh-temperature microwave-assisted UV digestion a promising sample preparation tech-nique for trace element analysisrdquo Analytical Chemistry vol 73no 7 pp 1515ndash1520 2001

[15] C Karunakaran and R Dhanalakshmi ldquoSemiconductor-ca-talyzed degradation of phenols with sunlightrdquo Solar EnergyMaterials and Solar Cells vol 92 no 11 pp 1315ndash1321 2008

[16] G Woldemichael T Tulu and G-U Flechsig ldquoSolar UVphotooxidation as pretreatment for stripping voltammetrictrace metal analysis in river waterrdquo International Journal ofElectrochemistry vol 2011 Article ID 481370 7 pages 2011

[17] G Woldemichael T Tulu and G Flechsig ldquoSolar UV-assistedsample preparation of river water for ultra-trace determinationof uranium by adsorptive stripping voltammetryrdquoMicrochimicaActa vol 179 no 1-2 pp 99ndash104 2012

[18] M Malaiyandi M H Sadar P Lee and R OrsquoGrady ldquoRemovalof organics in water using hydrogen peroxide in presence ofultraviolet lightrdquo Water Research vol 14 no 8 pp 1131ndash11351980

[19] E J Underwood Trace Elements in Human and Animal Nutri-tion Academic Press New York NY USA 4th edition 1977

[20] F W Sunderman Jr ldquoAnalytical biochemistry of nickelrdquo Pureand Applied Chemistry vol 52 no 2 pp 527ndash544 1980

[21] B Pihlar P Valenta and H W Nurnberg ldquoNew high-performance analytical procedure for the voltammetric deter-mination of nickel in routine analysis of waters biologicalmate-rials and foodrdquo Freseniusrsquo Zeitschrift fur Analytische Chemie vol307 no 5 pp 337ndash346 1981

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HCB (hexachlorobenzene) PCP (pentachlorophenol) TNT(135-trinitrotoluene) [5] and atrazine (a herbicide) [6]following absorption of 180ndash250 nm radiation

Under the influence of UV radiation different oxidantslike singlet oxygen [7] superoxide radicals and alkylperoxyradicals [8] and hydroxyl radical and hydrogen peroxide[9] are formed The subsequent reaction of these radicalswith organic matter is one of the natural ways of biodegra-dation in aquatic systems [9ndash12] Microwave-assisted high-temperature UV digestion procedure was developed for theaccelerated decomposition of interfering dissolved organiccarbon (DOC) prior to trace element analysis of liquid sam-ples such as industrialmunicipal wastewater groundwatersurface water body fluids infusions beverages and sewage[13] UV digestion instruments for theUVphotolysis of watersamples with a low to moderate amount of organic matterwere developed and commercially available for use Howeverthese instruments are relatively expensive which makes themdifficult to be used in some laboratories

Solar UV radiation was used in the presence of semi-conductors as catalysts in photodegradation of phenol [1415] We recently reported on a direct solar UV digestionmethod for stripping-voltammetric determination of zinccadmium lead and copper Only small amounts of oxidant(H2O2) were necessary for the pre-treatment of natural water

samples (riverwater) that contained lowDOCconcentrations[16] The addition of H

2O2to the samples before irradiation

increased the mineralization efficiency of the H2O2UV

system (88 of total organic carbon (TOC) reduction)compared with a UV-Only system (28 TOC reduction)at 4 hours of irradiation [16] Also uranium ultratracescould be detected this way [17] Therefore the applicationof solar radiation as a UV source for sample preparationhelps the application to be effective in many laboratoriesbecause of its natureThemethod is cheap clean mobile andenvironmentally friendly

Being essential elements cobalt and nickel become toxicat higher concentration because of their interaction withbiological systems [18] Nickel for instance needs exhaustiveecochemical and ecotoxicological investigations on its fateand behavior in ecosystem of terrestrial and aquatic envi-ronment It is among the toxic metals a significant topicof environmental surveillance food control occupationalmedicine toxicology and hygiene [19] Adsorptive strippingvoltammetry (AdSV) for cobalt and nickel elements was animportant advancement permitting lower detection limits[20] This involves a nonelectrolytic preconcentration step[21] In this case [20] the accumulation of Co and Ni asdimethylglyoxime (DMG) complexes in ammoniacal bufferat the hanging mercury drop electrode (HMDE) is followedby reduction of the adsorbed complex to the zero oxidationstate

In this paper both nickel (II) and cobalt (II) are deter-mined in river water samples by differential pulse adsorptivestripping voltammetric (DP-AdSV)method after the sampleswere digested by means of solar UV (UV-A) radiationin presence of hydrogen peroxide The effects of differentUV treatment protocols are also investigated by means ofpseudopolarography

Table 1 Instrumental parameters for AdSV experiments

Working electrode SMDEMeasurement mode DPPurging time 600 sPulse amplitude 005VDeposition potential minus07 VDeposition time 120 sEquilibration time 5 sStart potential minus08VEnd potential minus12 VVoltage step 0005VVoltage step time 03 sSweep rate 0013Vs

2 Experimental

21 Instrumentation A 120583Autolab potentiostat (Ecochemie)with General Purpose Electrochemical System (GPES) 49software package was connected to a Metrohm 663 VA Standwith an electrolysis cell equipped with a three-electrodesystemThe latter consisted of a HMDE as working electrodea glassy carbon counter electrode and a AgAgCl (3M KCl)reference electrode and was used for both the calibrationstudies and the pseudopolarographic experiments Differ-ential Pulse Adsorptive Stripping Voltammetric (DP-AdSV)method was used in both cases with the parameters given inTable 1

22 Reagents Ultrapure water (gt182MΩcmminus1 TOC lt2 120583gLminus1) was produced using an Ultra Clear system by SGWater GmbH Germany (now Evoqua Water TechnologiesLLC httpwwwwatersiemenscom) in order to prepareall solutions All reagents were obtained from certified man-ufacturers (Fluka Merck) and were delivered as analyticalgrade or ultrapure grade reagents (TraceSelect or Suprapur)where possible NH

3NH4Cl buffer (pH = 95) was prepared

as supporting electrolyte from ammonia solution (119908NH3 =25) and hydrochloric acid (119908HCl = 30) 01molLminus1 ofdimethylglyoxime (DMG) in ethanol and triethanolamine(TEA) in water (1 1) were prepared as complexing agentsin AdSVmeasurements Commercial 1000mgLminus1 stock solu-tions of the metals (Ni2+ and Co2+) were diluted as requiredfor standard additions 65 HNO

3was used to acidify the

water samples to pH 2 plusmn 02 (1mLLminus1) and 30 H2O2

was added to speed up the UV photocatalytic degradationprocess After the UV irradiation periods 10 120583L of 01molLminus1hydroxylammonium sulfate was added to 20mL of eachsample to remove newly formed nitrite and hypochlorite aswell as any remaining H

2O2

23 Sample Collection Preparation and Preservation Riverwater samples were collected in July 2011 based on the riverwater sampling protocols (EPA guidelines for regulatorymonitoring and testing water and waste water)The sampling















3NH4Cl (pH of
































Ni

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(a)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(b)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(c)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(d)









5 10 15 200

0

50

100

(a)

(b)

(c)

(d)

I(n

A)

c (120583gLminus1)


0

0

10

20

30

40

1 2 3 4 5 6

(a)

(b)

(c)

I(n

A)

c (ppb)




0

minus10

minus20


(a)

(b)

(c)

(d)

I pea

k(n

A)

Edep (V)




250 300 350

(a)(b)(c)

(d)(e)

(f)

(g)

04

03

02

01

00

Abso

rban

ce

Wavelength (nm)





4 Conclusions





Acknowledgments


References

































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of















3NH4Cl (pH of
































Ni

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(a)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(b)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(c)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(d)









5 10 15 200

0

50

100

(a)

(b)

(c)

(d)

I(n

A)

c (120583gLminus1)


0

0

10

20

30

40

1 2 3 4 5 6

(a)

(b)

(c)

I(n

A)

c (ppb)




0

minus10

minus20


(a)

(b)

(c)

(d)

I pea

k(n

A)

Edep (V)




250 300 350

(a)(b)(c)

(d)(e)

(f)

(g)

04

03

02

01

00

Abso

rban

ce

Wavelength (nm)





4 Conclusions





Acknowledgments


References

































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


























Ni

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(a)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(b)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(c)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(d)









5 10 15 200

0

50

100

(a)

(b)

(c)

(d)

I(n

A)

c (120583gLminus1)


0

0

10

20

30

40

1 2 3 4 5 6

(a)

(b)

(c)

I(n

A)

c (ppb)




0

minus10

minus20


(a)

(b)

(c)

(d)

I pea

k(n

A)

Edep (V)




250 300 350

(a)(b)(c)

(d)(e)

(f)

(g)

04

03

02

01

00

Abso

rban

ce

Wavelength (nm)





4 Conclusions





Acknowledgments


References

































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of








Ni

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(a)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(b)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(c)

Ni

Co

0

minus30

minus60

minus90


EVS AgAgCl (V)

I(n

A)

(d)









5 10 15 200

0

50

100

(a)

(b)

(c)

(d)

I(n

A)

c (120583gLminus1)


0

0

10

20

30

40

1 2 3 4 5 6

(a)

(b)

(c)

I(n

A)

c (ppb)




0

minus10

minus20


(a)

(b)

(c)

(d)

I pea

k(n

A)

Edep (V)




250 300 350

(a)(b)(c)

(d)(e)

(f)

(g)

04

03

02

01

00

Abso

rban

ce

Wavelength (nm)





4 Conclusions





Acknowledgments


References

































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


5 10 15 200

0

50

100

(a)

(b)

(c)

(d)

I(n

A)

c (120583gLminus1)


0

0

10

20

30

40

1 2 3 4 5 6

(a)

(b)

(c)

I(n

A)

c (ppb)




0

minus10

minus20


(a)

(b)

(c)

(d)

I pea

k(n

A)

Edep (V)




250 300 350

(a)(b)(c)

(d)(e)

(f)

(g)

04

03

02

01

00

Abso

rban

ce

Wavelength (nm)





4 Conclusions





Acknowledgments


References

































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



4 Conclusions





Acknowledgments


References

































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Documents

Research Article Solar UV-Assisted Pretreatment of …downloads.hindawi.com/journals/ac/2014/938419.pdfResearch Article Solar UV-Assisted Pretreatment of River Water Samples for the