Phan Tich Cr3-6 Apdc Khoang PH Pp XDRF

8/12/2019 Phan Tich Cr3-6 Apdc Khoang PH Pp XDRF

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VI simpozijHDZZ Stubike Toplic HR0500091

D E T E R M I N A T I O N OFC H R O M I U M ( II I ) ,CHROMIU M VI),M A N G A N E S E ( I I )AND M AN G ANESE VII) BY ED XRFM E T H O D

L u k a Mikeli1, Vinja Oreanin ,Stipe Luli and Mirta Rubi2'R u erBokovi Institute, Bijenika c. 54, HR 10000 Zagreb, Croatia2Facul tyof Science, Zvonimirova 8, HR 10000 Zagreb, Croatiae mail: lmikelic S>irb.hrINTRO U TIONIt iswellknown that metalexistsin several forms in nature, each one with aspecific bio toxicological activity. For this reason, it is necessary to use a sensitivemethod for determination different metal species. In solutions chromium mayexistin Cr( III) and Cr VI) oxidation state and manganese dominantly in Mn( I I ) andM n ( V II )oxidation state. In literature are various techniques for their determinationr ecommended.The most employed techniques include UV VIS spectrophotometry[1], high performance liquid chromatography HPLC) [2,3], capillaryelectrophoresis CE) [4], catalytic cathodic stripping voltammetry [5], flame andfurnace atomic adsorption spectroscopy AAS) [6 8] and mass spectrometry [9].In the spectrophotometric methods several conditions such as temperaturean d amount of reagent must be kept strictly constant in order to achieve goodreproducibility. Mayor disadvantage of these methods including AAS is inhandling complex sample matrices which have to be combined with a conversionstep of Cr( III) to Cr VI) or Mn VII) to Mn(I I ) . Separation of chromium andmanganese species using chromatographic techniques often results in inadequatesensitivity for trace concentration of Cr and Mn present in real samples because oflow sample loading. In all flow injection techniques the objective is to separate asingle analyt or group of analytes from interfering components or matrices, oftensimultaneously achieving some degree of preconcentration and therefore gainingsensitivity at the expense of separation power. Electrochemical methods werehighly sensitive, but disadvantage of these methods is in poor selectivity forchromium determination especially in the presence of other metals and also insmall linear dynamic ranges. Disadvantage of capillary electrophoresis is in opticaldetection because the optical path length diameter of the capillary) is generallyless than 100 um in order to favour better dissipation of Joule heat during theseparation process.We report here a method for the determination of chromium and manganesevalence states in liquid samples. The method is based on the preconcentration ofCr(I I I ) ,Cr VI),M n ( I I)and Mn VII) with APD C followed by the energy dispersiveX ray fluorescence ED XRF) analysis.

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XP RIM NT LAll solutions were prepared using analytical reagents grade chemicals anddistilled water.A PD C solution was prepared daily by dissolving APDC (Aldrich) indistilled water to produce 1% (w/v) solution. Cr(I I I ) , Cr(VI) , Mn( I I ) and Mn(VII )(1 ppm) stock solutions were prepared from C r ( N O3) 3, K2C r 2 0 7 , M n ( N O3) 2 an dK M n O 4 (Merck). One thousand micrograms per l iter solutions of EDTA wasprepared from KOMPLEKSAL II (Kemika). One hundred microgram per l i t restandard solutions of F e2+ , M n2+ , V4+ were prepared from Merck standard solutionsfor AAS.O n e hundred millilitres of a solutions containing 1000 ug/L of Cr( III) orCr (VI) o r M n ( I I ) or M n( VII) was adjusted to pH values 3 11 by addinghydroch loride acid and am m on ium hydroxide to estimate th e effect of pH on therecovery of chrom ium and m anganese species. All pH m easurem ents were m adewith M ettler Toledo d igital pH m eter. The influence of organic m eter, carbonate ormetal ion s on the recovery of each specie over whole pH ran ge was also tested.This was carried out to stimulate conditions occurring in natural waters. After pHadjustment 2 mL of 1% APDC solution was added into each flask. Aftercomplexation lasted for 20 minutes, the suspension was filtered through MilliporeHAWP (poresize 0.45 um, diameter 25 mm). A Mill ipore micro fil tration systemwas used for that purpose. Prepared thin targets were air dried, protected by thinmylar foil, inserted into a plastic carrier and placed above the Xray source of theXray spectrometer.All targets were analysed with energy dispersive Xray fluorescence( E D X R F ) [10]. Instrumental and measurement conditions were presented in Table1. Spectrums were collected by Genie 2000 software (Canberra). Spectral datawere analysed by aWinAxil software (C anberra). Th e IR spectra of all com poun dswere recorded using PerkinElmer FT Spectrum RX1 as KBr pellets in the regionof 4000450 cm 1.

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Table1 .Excitation,detection and geometry conditionused in conducted E D X R Fmeasurementco1oXUJ

ion

tt

LQ

nt

ror

u

So ur c eH a l f liveC al ib ra t ion d a t eCal ibra ted ActivityCrys ta lCrystal thicknessCrystal densityCrystal dead layerC o n t a c tC o n t a c t t h ic knes s

C o n t a c t dens i tyW i n d o wWind o w t h ic knes sWind o w d ens i t yF W H M for 5.9 KeV 5 5F eSo ur c e / sa mpl e d i st a nc eIn c id en t AngleSample detec tor d is tanceEmerging angle

1 0 9 C d46 4 days12/03/2001594 .00 M B qSi3.00 mm2.34 g/cm 30.300 urnAu20.000 n m

19.30 g/cm 3Be25.400 u m1.85 g/cm 3165 eV1 c m49 . 7 6 2.5 cm74.05

R E S U L T S AN D D I S C U S S I O NT h e effec t of pH between 3 and 11 on the recovery of Cr( I I I ) / C r(VI) andM n ( I I ) / M n ( V I I ) in the absence of other substances is presented in Figure 1. Them a ximu m r ec o ver y o f Cr (VI ) wa s o b t a ined a t pH 4 . Th e c o mpl exa t io n wi t h AP D Cwas irregular in the pH range 59 whi le a t pH 10 and 11 no complex format iono c c u r r e d a t a l l . On the cont rary , the maximum recovery of C r ( I I I ) was obta inedexact ly a t pH 10 (98%). The maximum recovery of M n ( I I ) was obtained at pH 10whi le m a ximu m r ec o ver y o f M n( VI I ) wa s o b t ained at pH 8 (97 ,5%) .Spect ra of products obta ined via preconcent ra t ion with APDC a t pH 10 f roms o l u t io ns c o nt a in ing mix t ur e o f C r ( I I I ) a nd Cr (VI ) salts an d C r ( I I I ) salt only areident ical . The charac ter is t ic fea ture of spec t ra of both compounds is very s t rongan d broad band in the region of 3 4 0 0 3 5 0 0 cm ' tha t can be assigned t o O Hst re tch ing and very poor ' f inger pr int ' region which indica te tha t no organic materis bonded to Cr ( I I I ) . Therefore , i t can be concluded tha t a t pH 10 dominants pec imen i s C r ( O H )3 a nd t h a t no C r ( I I I ) P D C complex is formed, which is ina c c o r d a n c e with ca lcula ted d is t r ibut ion of inorganic C r ( I I I ) species at different pHvalues [11] .

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Spectra of compounds prepared via preconcentrat ion with APDC at pH 4from solutions containing mixture of Cr( III) and Cr(VI)salts and Cr(VI) salt onlywere compared mutual ly as well as with spectra of free APDC. IR spectra ofprepared compounds obtained in both cases are equivalent. Very strong band,correspon ding to N H st re tching p ositioned at 2956 cm 1 in the spectra of freeA P D C , in the spectra of Cr(VI)products disappears and suggests that complexC r ( V I ) P D C is formed. F urtherm ore, stron g doublet observed at 1001, 990 cm 1 inthe spectra of free APDC assigned to CS stretching becomes strong single bandposit ioned at 1005 cm 1 in the Cr(VI)PDC spectra along with shift of the bandcorresponding to CN st re tching from 1413 (APDC) to 1485 cm 1 (C r ( VI ) P D C )indicating that l igand (PD C ) is bidentate [12].Spectars of manganese products obtained via preconcentration with APDCshows sam e results as spectars of chrom ium com pou nd s.

Also, same method was used to investigate preconcentration of manganeseand chromium species with DTPA. Results for the recoveries are lower then forA P D C method .A characterist ic of C r(III ) /C r(VI) and M n(II) / M n(VII) to create com plexeswith AP D C at different pH ranges m akes possible to separate the species. Resultspresented here show that complicated and t ime consuming methods could besuccessfully replaced by a simple aswell as rapid m ethod based on precon cetrationof different species with nonspecific chelating agent ammoniumpyrrol id inedith iocarbamate . The major advantage of EDXRF method overcommonly used methods is simultaneous analysis ofwide ranges of metals in thecomplex environmental samples without separation of species or any kind ofpretreatment.

1 0 0 9 0

7 0 2 6 0 5 0 4 0

3 0 2 0 1 0

0

Cr(lll)*APDC\ * C r ( V I ) + A P D C\ / \\ A/\ / \ // Y/ Av A/ \ J \ v/ \

7PH

/ \/ \ / *

9 11

Figure I . Percentage of recovery ofC r(I I I ) /C r(VI)and Mn(II ) /Mn(VII)by APD Cfor different pH values

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R F R N S[ I ] Llobat Estelles M, MauriAucejo AR, Lopez Catalan MD . J Anal Chem 2001; 371:358.

[2] Ou Yang GL, Jen JF . Anal Chim Acta 1993; 279: 329.[3] Collins CH, Pezzin SH, Rivera JFL, Bonato PS, Windmeller CC, Archundia C,

Collins KE. J Chromatogr A 1997; 789: 469.[4] Himeno S, Nakashima Y, Sano K. Anal Sci 1998; 14: 369.[5] Li Y,XueH . Anal Chim Acta 2001; 448: 121 134.[6] M.J. Marques, A. Morales Rubio, A. Salvador, M. De la Guardia, Talanta 2001;

53:1229.[7] Gaspar A, Posta J. Anal Chim Acta 1997; 354: 151.[8] Pasullean B, Davidson CM, Littlejohn D. J Anal Atom Spectrom. 1995; 10: 241.[9] Andrle CM, Jakubowski N, Broekaert JAC. Spectrochim Acta B 1997;52: 189.[10] Oreanin V, Mikeli L, Luli S, Rubi M.Anal Chim Acta 2004;527: 125 129.[ I I ] Sperling M, Xu S,WelzB. Anal Chem 1992; 64: 3105.[12] Bernal C, Almeida Neves E, Cavalheiro ETG. Thermochim Acta 2001; 370: 50.ABSTRACT

This paper describes E D X R F , a quick, sensitive and selective method fordetermining C r ( I I I ) , Cr VI), M n ( I I ) and Mn VII) in environmental and industrialliquid samples via preconcentration with am mon ium pyrrolidinedithiocarbamate( A P D C ) and diethylenetriam inepen taacetic acid D TP A). The effect of pH in therange of 3 11 on the recovery of C r ( I I I ) , Cr VI), M n ( I I ) and M n VII ) wasinvestigated separately and in combination . The influence of organic matter,carbonate species and elements V and Fe was also tested on the recovery of eachc h r o m i u m and man ganese species separately/ in com bination) over the whole pHrange in order to simulate conditions in natural waters that usually contain a certaina m o u n t of dissolved organic matter and carbonate ions. Character istic of differentspecies to create complexes with APD C and D TP A in the different pH rangesmakes possible to separate those two species. All created complexes of C r ( I I I ) ,C r ( V I ) , M n ( I I ) and Mn VII I) with APD C and DT PA were character ised by IRspectroscopy.

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Phan Tich Cr3-6 Apdc Khoang PH Pp XDRF