A Simple Electrophoretic Method for the Simultaneous Determination of Chromium and Vanadium in Real and Environmental Samples

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1 Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27) 54 ISSN X Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27) A Simple Electrophoretic Method for the Simultneous Determintion of Chromium nd Vndium in Rel nd Environmentl Smples M. Jmluddin Ahmed * nd Yi Chen Lortory of Anlyticl Chemistry for Life Science, Institute of Chemistry, Chinese Acdemy of Sciences, Beijing-18, P. R. Chin Astrct A very simple, selective nd highly sensitive cpillry electrophoretic method for the simultneous determintion of chromium(iii) nd vndium(v) with Mo(VI)-P(V) regent hs een developed. A Mo(VI)-P(V) regent rected with mixture of trce mounts of chromium(iii) nd vndium(v) to form the stle heteropolynions in.1m cette uffer (ph 2.) t room temperture(25±5 C). Both nionic forms of chromium(iii) nd vndium(v) cn e determined simultneously y cpillry electrophoresis with direct UV detection t 254nm. The pre-column complex formtion rection is instntneous nd sornce remins stle for 24h. Liner clirtion curves were otined in the concentrtion rnges of.6 6 mgl -1 nd.5 8 mgl -1 of Cr(III) nd V(V), respectively; the detection limits were 6. µg L -1 nd 5. µg L -1, respectively. The influence of severl experimentl prmeters on oth sensitivity nd efficiency ws investigted. The interference from over 5 ctions, nions nd complexing gents hs een discussed t 1 mgl -1 of Cr nd V, respectively. The unique selectivity nd sensitivity of the method llowed its direct ppliction to the determintion of Cr nd V in complex mtrices of certified reference mterils nd synthetic sewter.. The developed ws lso used successfully in the determintion of chromium nd vndium in environmentl wters (tp nd lke). The method hs high precision nd ccurcy (s =±.2 for.5 mg L -1 ). Keywords: Cpillry electrophoresis; Mo(VI)-P(V) regent; chromium nd vndium; lloy; steel; environmentl wters Introduction Chromium nd / or vndium in trce mounts is importnt industrilly [1], s : iologicl nutrient [2], epidemiologicl preventive[3], toxicnt [4], environmentl pollutnt [5] nd occuptionl hzrd [6]. Therefore, the ccurte determintion of the metl t trce nd ultr-trce levels is importnt. Simultneous determintion of chromium nd vndium in complicted mtrices is very difficult tsk tht chieved using sophisticted nd / or high cost instruments such s nodic stripping voltmmetry with ICP-MS detection [7], ICP-AES [8], NAA [9], HPLC [1], XRF [11] nd AAS [12]. However, the reltively *Corresponding Author E-mil: mjhmed_d@yhoo.com high costs [7-12], high detection limits [1-12] nd poor recoveries nd precisions re common disdvntges. Moreover, such methods must e comined with prior pre-concentrtion, ion exchnge nd / or solvent extrction seprtion techniques [8,1,11]. Hence the need for simple, low cost, sensitive nd highly selective method is cler. Cpillry Electrophoresis (CE) is eing incresingly pplied for the determintion of metl ions, primrily ecuse of its gret flexiility nd esy implementtion [13]. Seprtions of metl ions tht exist in free, uncomplexed form re comprtively rre in the prctice of CE ecuse the solute moility

2 52 Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27) vlues of most of the metl ions in their free form do not differ enough from one to nother to envision electrophoretic seprtions of prcticl interest. Oviously, complextion presents the most vlule pproch for performing metl specition nd offers powerful mens of mnipultion nd seprtion selectively. The so clled molydenum lue method hs een used for the colorimetric determintion of inorgnic oxonions. A modified of the method is known s the Mo(VI) Mo(V) regent method [14]. However, from recent studies [15, 16] the formtion of different types of polyoxometlte ws possile. These studies showed tht the so-clled lcunry molydophosphte complex [H 3 PMo 11 O 39 ] 4- ws kineticlly stle t low concentrtion of Mo(VI) nd P(V) in queous solutions [17, 18]. A comintion of these findings prompted us to develop new nlyticl method with the use of Mo(VI) P(V) regent, in which the lcunry molydophosphte, [H 3 PMo 11 O 39 ] 4- exists s predominnt. In the Mo(VI) P(V) regent method, oxonions to e determined re incorported in the peripherl structure of the molydophosphte complex. The present study ws undertken to pply the Mo(VI)-P(V) regent method to simultneous CE determintion of chromium(iii) nd vndium(v), ecuse their yellow color complexes were kineticlly stle nd possessed different moilities. The method ws sed on the rection of non-sorent Mo(VI) P(V) regent in.1 M cette uffer of ph 2. with Cr(III) nd V(V) to produce highly UV-sorent yellow complex product, followed y direct mesurement of the sornce in queous solution. With suitle msking, the rection cn e mde highly selective nd the regent lnk does not show ny UVsornce. Experimentl Instrumenttion The cpillry electrophoresis experiments were performed with P/ACE-25 system (Beckmn Instruments, Fullerton, CA, USA) equipped with UV detector. All seprtions were crried out on fusedsilic cpillry of 4 47 cm 5 µm i.d. Seprtion ws performed with cthode t the injection side. Smples were injected in the hydrodynmic mode y pplying pressure of 3.44 kp. The temperture of the cpillry ws kept t 25 C using thermoregultion equipment of the instrument. Electropherogrms were recorded y vrying the pplied voltge (-5 to -25 kv). Optimum seprtion with miniml nlysis time ws otined t the pplied voltge of -15 kv. Lower pplied voltge incresed the nlysis time nd rodened the pek-shpe. At higher pplied voltge, the seline ecme incresingly noisy, proly owing to the Joule heting effect. ph mesurement ws mde using ph-mv meter model PHS 3B with comintion electrodes. A typicl commercilly ville [13] CE instrumentl system is shown in Figure 1. Figure 1. Typicl CE seprtion system. Regents nd solutions All chemicls used were of nlyticl-regent grde or the highest purity ville. Douly distilled wter, which is non-sorent under UV-rdition, ws used throughout. Glss vessels were clened y soking in cidified solution of KMnO 4, followed y wshing with concentrted HNO 3, nd were rinsed severl times with high purity distilled wter. Stock solutions nd environmentl wter smples (1-mL ech) were kept in polypropylene ottle contining 1-mL of concentrted HNO 3. A stock solution of 5 mm Mo(VI) nd 5 mm P(V) ws prepred y dissolving requisite mounts of N 2 MoO 4. 2H 2 O nd NH 2 PO 4. 2H 2 O, respectively. The solutions were stle for t lest one month when stored in ottle t 4 C. A stock solution of 1M cette uffer (running uffer) (ph 2.) ws prepred y pproprite mounts of CH 3 COOH nd CH 3 COON solution nd its ph ws djusted to 2. y ph meter. A 1 ml mount of stock stndrd solution of 1 mgml -1 of Cr(III) ws prepred y dissolving mg of Cr(NO 3 ) 3. 9H 2 O in douly distilled wter nd 1 ml mount of stock solution (1mg ml -1 ) of V(V)

3 Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27) 53 ws prepred y dissolving mg of NH 4 VO 4 in douly distilled wter contining 1-2mL of nitric cid(1+1). More dilute stndrd solutions were dily prepred from these stock solutions s nd when required. The following working solutions were used:. 2 mg ml -1 of EDTA nd 2. mg ml -1 of As III nd 1-mL stock solution(1mg ml -1 ) of Cr VI or V IV ws prepred from K 2 Cr 2 O 7 or VOSO 4. nh 2 O, respectively. Also, 5% solution of NH 4 OH. Other solutions: Solutions of lrge numer of inorgnic ions nd complexing gents were prepred from their Anlr grde or equivlent grde wter solule slts. Homogenized nd finlly powdered certified reference mterils from Beijing NCS Anlyticl Instruments CO. Ltd, Beijing, P.R. Chin, were used s received. Procedure A volume of 1-1.mL of queous solution contining.5 8 µg of vndium(v) nd.6 6 µg of chromium(iii) in 1-mL clirted flsk ws mixed with 1-mL of 5 mm of Mo(VI) nd 1-mL of 5 mm P(V) followed y the ddition of 3-7-mL (preferly 5-mL) of 1M cette uffer (ph 2.). The mixture ws diluted to up to mrk with doule distilled wter nd it ws left stnding for 2 min t room temperture (25±5 C). Before CE mesurement, the cpillry ws filled with.1m cette uffer (ph 2.) (running uffer), nd.1m NCl solution ws introduced for 3s s leding electrolyte for the trnsitionl isotchophoresis effect [19]. The smple ws introduced into cpillry for 3-2 s (preferly 1s) nd the sornce ws mesured y UV-detection t 254 nm. The Mo(VI) P(V) regent does not show ny sornce t UV-region in the sence of V(V) nd Cr(III). The concentrtions of V(V) nd Cr(III) were evluted from the pek heights of the signl y using the clirtion curves prepred with the stndrd solutions. Results nd Discussion Optimiztion of the CE system Preliminry tests were crried out with the id of different flow ssemlies to select the optiml CE conditions. In order to optimize the CE conditions, the influence of the hydrodynmic nd chemicl prmeters on the mgnitude of the pek height, the shpe of the pek nd reproduciility of the results were studied for test solution consisting of 5. mm Mo(VI),.5 mm P(V), 1 mgl -1 of oth V(V) nd Cr(III). Tle1 shows the results optimiztion of working conditions. Tle 1. Selected chemicl nd CE prmeters otined with optimiztion experiments Prmeter Studied rnge Selected vlue Wvelength filters ( mx) / nm 2, 214, 254, Acidity / M H 2SO (preferly M) ph of running uffer (.1M cette uffer) Length,cm(effective length, cm) I.D. m 47 4cm (25-75) m 47 4cm 5 m Applied pressure for smple injection / kp Applied voltge kv Injection time of smple / sec Injection time of.1 NCl / sec Concentrtion of regent (M) CH 3COOH CH 3COON Mo(VI) P(V) NCl

4 54 Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27) 5 4 ma.u Time / min Figure 2. An electropherogrm for test solution consisting of 5. mm Mo(VI).5 mm P(V).1M cette uffer (ph 2.) contining 1. mgl -1 V(V) nd 1. mgl -1 Cr(III). The running uffer;.1m cette uffer (ph 2.) () V(V) nd () Cr(III) t 254 nm (pplied Voltge = - 15 kv). Preliminry experiments hve shown tht proper choice of migrtion uffer is importnt for the seprtion of Cr(III) nd V(V). Trtrte, formte, citrte, cette, mlonte nd monochloro cette uffer solutions of ph 2-4 were exmined, nd the est results regrding the sensitivity nd pek shpes were otined with the use of.1m cette uffer s oth smple nd running uffers. The effect of the uffer ph on the electropherogrm is shown in Figure 4. At ph 2. (Figure 2), the first pek is due to [P (V v Mo 11 ) O 4 ] 4 nd the second is due to the [P(Cr III Mo 12 ) O 4 ] 3- nion; no peks due to free isopolymolydte species were oserved. The ddition of the Mo(VI)-P(V) regent to the running uffer is not required, ecuse the [P(V V Mo 11 )O 4 ] 4- nd [P(Cr III Mo 12 ) O 4 ] 3- complexes were so kineticlly stle nd no degrdtion occurred during migrtion in the cpillry. The electropherogrm is shown in Figure 2 pek () is due to [P(V V Mo 11 )O 4 ] 4-, nd pek () is due to [P(Cr III Mo 12 )O 4 ] 3- which migrtes fster through the cpillry thn [P(Cr III Mo 12 ) O 4 ] 3-, ecuse the former crries the greter negtive chrge of -4. Both peks were shrp nd well seprted. Figure 3 shows the whole spectr of PCr III Mo 12 nd PV V Mo 11. Different wvelengths (e.g. 2, 214, 22, 254, 28, 3nm) were tested, 254nm ws found to e est wvelength for the system. Figure 3. UV-visile spectr for M of Mo(VI) M of P(V) system contining, 1 mgl -1 () Cr III nd () V V in n queous solution of ph 2., pth length 1. cm. The respective peks heights were plotted ginst the uffer ph nd the results re shown in Figure 4. The peks height for [P(V V Mo 11 )O 4 ] 4- ws gretest round ph the corresponding vlue for [P(Cr III Mo 12 )O 4 ] 3- ws prcticlly constnt in the ph rnge of As result, ph 2. ws chosen s eing optionl for the simultneous CE determintion of Cr(III) nd V(V) t 254 nm.

5 Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27) 55 V(V) Cr(III) A.U Figure 4. Reltionship etween the smple ph nd the pek-heights for () V(V) nd () Cr(III). The test solution: M of Mo(VI) M P(V).1 M cette uffer contining 1 mg L -1 of V(V) nd Cr(III). The running uffer,.1m cette uffer (ph ws djusted to e the sme s the smple uffer). ph After stnding for some period (2 min) t room temperture, the test solution ws introduced into cpillry thermo stted t 25±5 o C; the period is denoted s the rection time. The pek heights for oth chromium(iii) nd vndium(v) were mesured s function of the rection time, nd re shown in Figure 5. The pek-heights for the Cr(III) specition were not ffected y the vrition in the rection time nd temperture. On the other hnd, the pek-height for the V(V) species with the rection time t room temperture (25±5 o C), nd ttined constnt vlue t rection time of 2 min. At temperture of 25 o C, however, the pek height ws independent of the rection time. The temperture of the cpcity system ws set t 25 o C, ecuse reproducile results were otined even when the test solution ws introduced immeditely fter preprtion. The rection is rpid. A constnt mximum sornce ws otined just fter 2 min of dilution to volume nd remined strictly unltered for 24 h Figure 5. In order to optimized the Mo(VI) concentrtion in smple solution to e determined, test solutions were prepred y vrying the Mo(VI) concentrtion ( M) while keeping [Cr(III)=V(V)]= 1mgL -1 in.1m cette uffer (ph 2.). The test solutions were introduced into the cpillry nd electropherogrms were recorded. In series of electrophoretic mesurements,.1m cette uffer (ph 2.) ws lso used s migrtion uffer. The optimum concentrtion of Mo(VI) ws found to e M. Similrly the optimum concentrtion of P(V) ws found to e M ( M). A length 4 47 cm 5 m i.d. fused silic cpillry for the seprtion, 3.44KP pressure for the smple injection; 1 to- 25kV(preferly 15kV) pplied voltge; 3-2 second (preferly 1sec) for smple injection time, min (preferly 7.4 min) for Cr nd min (preferly 9.5) for V were selected, these eing compromise etween the smpling rte nd the height of the pek Figure 2. A well-known eqution for photometric nlysis in very dilute solution ws derived from Beer s lw. The effect of the metl concentrtion ws studied over.1 1 mg L -1 for oth Cr(III) nd V(V) distriuted in two different sets (.1 1. nd 1 1 mg L -1 ) for convenience of mesurement. The pek heights showed Figure 6 & 7 liner dependence on the concentrtion of Cr(III) or V(V) in rnge of.6 6 mgl -1 or.5 8 mg L -1, respectively. The correltion coefficients re.9998 nd.997 for Cr(III) nd V(V), respectively.

6 56 Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27).8 V Cr A.U Time / min Figure 5. Pek - height s function of time for M Mo(VI) M P(V).1M cette uffer (ph 2.) system t room temperture(25±5) C contining 2 mg L -1 () V(V) nd () Cr(III) in n queous solution t 254 nm V(V) Cr(III) A. U [ Cr(III)] or [V (V)] / mgl -1 Figure 6. Clirtion grphs: ().5 1 mgl -1 of V(V) nd ().6-1 mgl -1 Cr(III).

7 Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27) 57 V(V) Cr(III) A.U [ Cr(III) ] or [ V(V) ] / mgl -1 Figure 7. Clirtion grphs: () 1 8 mgl -1 of V(V) nd () 1-6 mgl -1 Cr(III) Effect of foreign ions The interference of severl ions which my occur in environmentl smples ws studied y using solution contining mixture of Cr III nd V V t concentrtion of 1 mg L -1, dding where the reltive error reched vlue of out 5%. The errors were clculted y compring the pek height to tht otined fter injection of n queous solution of Cr III nd V V contining no interfering ions, s reference. The results re summrized in Tle 2. As cn e seen, lrge numer of ions hd no significnt effect on the determintion of Cr III nd V V. The most serious interference ws from V(IV) nd Fe(III) ions. There is possiility tht these metl ions cn lso rect with Mo(VI) in migrtion uffer of ph 2. Their presence cuses no serious errors ecuse the moility of the V(IV) nd Fe(III) complexes re different from those of the Cr(III) nd V(V). However, greter tolernce limits for these ions cn e chieved y using severl msking methods. In order to eliminte the interference of V(IV) nd Fe(III) ions, trtric cid, EDTA or chloride cn e used s msking gents. Evlution of the Method The reproduciility of the proposed procedure nd smple throughput were determined y repeted injection of smple contining 1 mg L -1 Cr III nd V V. The RSD (n=5) ws 2-.1% for.6-6. mg L -1 of Cr III nd.5-8. mg L -1 of V V indicting tht this method is highly precise nd reproducile. The clirtion grphs otined from the pek heights were rectiliner for 6 g L -1 to 6. mg L -1 of Cr III nd 5 g L -1 to 8. mg L -1 of V V, respectively. The correltion coefficients re.9998 nd.997 for Cr III nd V V, respectively. The limit of detection of 6. g L -1 for Cr III or 5. g L -1 for V V, for the photometric detection ws clculted s the mount of metl ion, which produced pek-height response equl to three times the detector seline pek-to-pek noise. Importnt fetures of the proposed method for simultneous determintion of Cr III nd V V re summrized in Tle 3. The nlyticl results must e evluted with regrd to the vlidity of the nlyticl method. Poor nlyticl qulity my led to flse conclusions [2].

8 58 Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27) Keeping this in our mind the vlidity of our method ws tested y nlyzing severl Stndrd Reference Mterils, recovery studies nd lso compring the results with conventionl nlysis (spectrophotometry). The performnce nd reproduciility of the proposed method re lso shown in Tle 4-5. The reliility of the proposed procedure ws lso ssessed y Certified Reference Mterils. The results for totl Cr III or V V were in good greement with certified vlues (Tle 4). The method ws lso tested y nlyzing synthetic sewter contining stndrd Cr III nd V V (Tle 5). The reliility of the proposed Procedure ws lso tested y performing recovery studies. The verge percentge recovery otined for the ddition of Cr III nd V V spike to some environmentl wter nd synthetic se wter smples were quntittive s shown in Tle 5. The results of tp nd lke wter nd synthetic se wter nlyses y the present method were in excellent greement with those otined y spectrophotometry (Tle 5). The precision nd ccurcy of the method re stisfctory. Applictions The proposed method ws used to determine the totl chromium nd vndium contents in numer of certified reference mterils (lloys nd steels) (Tle 4). The method ws lso successfully pplied to the simultneous determintion of chromium(iii) nd vndium(v) content in synthetic se wter (Tle 5). The method lso extended to the simultneous determintion Cr III nd V V in numer of environmentl wters. The smples were spiked with the concentrtion of Cr III nd V V nd recoveries determined (Tle 5). The results of nlyses of environmentl wters y our procedure were in excellent greement with those otined y spectrophotometry (Tle 5). Determintion of totl chromium nd vndium in certified reference mteril A.1g mount of n lloy or steel smple ws ccurtely weighed into 15 ml Teflon eker nd digested following method recommended y Vn Loon et l [21]. the eker with the testing mteril nd mixture 1 ml of HF 2 ml HClO 4 nd 1 ml HNO 3 were wrmed slowly on hot plte until complete dissolution ws chieved. Then the temperture ws incresed to out 2 o C to evporte the excess cid. The smple ws cooled nd dissolved the slt in 1 ml of 1% H 2 SO 4 y wrming. One ml of the working As III solution ws dded to the resulting solution nd oiled gently for 5 min to reduce Cr VI to Cr III. Tle 2. Tolernce limits of foreign ions Species x Tolernce rtio x/cr III (w/w) Tolernce rtio x/v V (w/w) Ascoric Acid 1 1 Ammonium(I) 5 5 Arsenic (III) 5 5 Arsenic (V) 5 5 Aluminum 1 1 Azide 5 5 Brium 1 1 Bismuth (III) 5 5 Bromide 1 1 Citrte 1 1 Chloride 1 1 Trtrte 1 1 EDTA 1 1 Fluoride 1 1 Chromium (VI) 1 +c 1 +c Colt (II) 5 5 Colt (III) 1 1 Cdmium 1 1 Clcium 1 1 Cesium 1 1 Copper (II) 1 1 Iodide 1 1 Oxlte 1 1 Nitrte 5 5 Iron (II) 1 +c 1 +c Iron (III) 5 5 Led (II) 1 1 Mngnese (II) 5 5 Mercury (II) 5 c 5 c Nickel (II) 5 5 Potssium 1 1 Sodium 1 1 Tin (II) 5 5 Thiocynide 1 1 Thllium(I) 5 5 Selenium(IV) 5 5 Tungsten(VI) 1 1 Vndium (IV) 2 +c 2 +c Zinc 1 1 Tolernce limit defined s rtio tht cuses less thn 5% interference With 1mg/ L EDTA c With 1mg/ L Chloride d With 1mg/ L Trtrte

9 Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27) 59 completely which hs no reducing effect for V V [22]. The ph of the resulting solution ws djusted to 2. ±.1 using the dilute NH 4 OH solution. The content of the eker ws filtered through Whtmn no.4 filter pper into 25-mL clirtion flsk nd mde up the mrk with deionized wter. A suitle liquot of the ove-mentioned solution ws tken into 1-mL clirted flsk nd chromium(iii) nd vndium(v) content ws determined, s descried under procedure using ttrte or EDTA s msking gent. Bsed on five replicte nlyses, the verge chromium nd vndium concentrtion determined y the CE method ws in close greement with the certified vlues. The results re given in Tle 4. The electropherogrms for smple 1 nd smple 2 re shown in Figure 8 & 9. Tle 3. Anlyticl fetures of the proposed method Prmeter Selected vlue for Chromium (III) Selected vlue for Vndium (V) ph / Acidity (M) 2. /.1 M 2. /.1 M Time 5 min 24 h (preferly 25 min) 25 min 24 h (preferly 25 min) Temperture / C (Temperture of cpillry) 25 ± 5 25 ± 5 Seprtion time / min (preferly 7.4) (preferly 9.5) Regent [ molr rtio, P(V) : Mo (VI) ] 1 : 1 1 : 1 Liner rnge / mg L Detection limit / µg L Quntiztion / µg L Reproduciility(% RDS) Correltion coefficient (R 2 ) Tle 4. Recoveries of totl chromium nd vndium for certified reference mterils. Certified reference mteril (composition,%) Chromium,% Certified vlue Found c (n=5) Recovery ± s, (%) Certified vlue Vndium,% Found c (n=5) Recovery ± s, (%) GSBH , Cr12Mo1V- Die steel C=1.5, Mn=.155, P=.188, S=.89, Si=.235, Cr=11.63, Ni=.95, Cu=.82, Mo=.96, V=.411, Co=.2, Sn= ± ± 1.5 BH 113-1, 9Cr17MoVCo-Hightensile steels. C=.9, Cr=16.3, Si=.44, Mo=.52, Mn=.81, P=.42, V=.24, S= ± ± 2. This CRMs were otined from Beijing NCS Anlyticl Instruments Co. LTD., P.R. Chin. The mesure of precision is ± s. c Averge of five determintion.

10 6 Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27) ma.u Time / min Figure 8. An electropherogrm for Die steel smple solution contining of () 11.6 mgl -1 of Cr(III) nd.41 mgl -1 V(V). The running uffer;.1m cette uffer (ph 2.)) t 254 nm. Electrophoretic conditions re identicl to those shown in Fig ma.u Time / min Figure 9. An electropherogrm for High tensile steel smple solution contining of () 16.3 mgl -1 Cr(III) nd ().24 mgl -1 of V(V). The running uffer;.1m cette uffer (ph 2.)) t 254 nm. Electrophoretic conditions re identicl to those shown in Fig. 2.

11 Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27) 61 Determintion of totl chromium nd vndium in environmentl wter smple Ech filtered (with.22µm memrne filter) environmentl wter smple (5 ml) ws evported nerly to dryness with mixture of 5 ml of concentrtion H 2 SO 4 nd 1 ml of concentrted HNO 3 in fume cupord, following method recommended y Mitr [23] nd ws then cooled to room temperture (25±5 o C). The residue ws then heted with 1 ml of deionized wter in order to dissolve the slts. One ml of the working As III solution nd 5 ml of.1m cetic cid were dded to the resulting solution nd oiled gently for 5 min to reduce Cr VI. The ph of the finl solution ws djusted to 2.±.1 using dilute NH 4 OH solution in presence of 1-2 ml of.1% (w/v) EDTA or trtrte solution. The resulting solution ws filtered nd quntittively trnsferred into 25-mL clirted flsk nd mde up to the mrk with deionized wter. A liquot (1-2 ml) of this preconcentrted wter smple ws pipetted into 1-ml clirted flsk nd chromium nd vndium contents ws determined s descrie under procedure using EDTA or chloride s msking gent. The proposed procedure for the simultneous electrophoretic determintion of chromium nd vndium ws pplied to the nlysis of synthetic se wter. Synthetic se wter ws prepred ccording to the procedure recommended y [24]. A typicl electropherogrm for V v nd Cr III in spiked synthetic se wter is shown in Figure 1. The results of environmentl nlyses y the cpillry electrophoretic method were found to e in excellent greement with those otined y spectrophotometry. The nlyses of environmentl wter smples from vrious sources for totl chromium nd vndium re given in Tle 5. Tle 5. Determintion of chromium nd vndium in some environmentl wter smples. Smple Tp Wter Concentrtion of chromium / gl -1 Concentrtion of vndium / gl -1 Proposed CE method (n=5) Spectrophotometry (n=5) Proposed CE method (n=5) Spectrophotometry (n=5) Added Found Recovery ± s Found Add ±s Recovery % Found Recovery ±s Found Recovery ±s % ed % % ±.5 54 ± ±.6 53 ± ±.7 58 ± ±.5 55 ± Well Wter ±.8 59 ± ±.6 57 ± ±.7 58 ± ± ± Lke Wter ±.9 51 ± ± ± ± ± ± ± Synthetic Se Wter c ±.5 53 ± ±.5 5 ± ± ± ±.4 52 ± Averge of five replicte determintions Weiming Lke, Peking University Cmpus, Beijing. c Composition of synthetic se wter 24 : NCl=24.72 gl -1, KCl=.67 gl -1, CCl 2,2H 2O=1.36 gl -1, MgCl 2,6H 2O=4.66 gl -1, MgSO 4.7H 2O=6.29 gl -1, NHCO 3=.18 gl -1, Tris HCl(pH 8.2)=.5M, H 2O= mde up to 1L. In order to evlute the quntittive performnce of the method, severl rel smples were nlyzed y using CE nd conventionl spectrophotometric methods. For the determintion of totl chromium, 1,5-diphenylcrzide[25] nd for vndium, 5,7-diromo- 8-hydroxyquinoline methods [26] were used, respectively. The results otined y oth techniques re compred in Tle 5. Finlly, the recovery tests were performed for smples spiked with metl species t vrious concentrtion levels. The men recoveries were in the rnge 97-15% for ll nlytes studied. These results illustrte tht CE offers promise for the simultneous determintion of metl ions in rel smples.

12 62 Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27) ma.u Time / min Figure 1. An electropherogrm for test solution consisting of synthetic se wter nd M Mo(VI) M P(V).1M cette uffer (ph 2.) contining 1. mgl -1 V(V) nd 1. mgl -1 Cr(III). The running uffer;.1m cette uffer (ph 2.) () V(V) nd () Cr(III) t 254 nm ( pplied Voltge = - 15 kv ) [ Recovery = 11% for V(V) nd 13% for Cr(III), n=3]. Conclusions The results of this work demonstrte tht Mo(VI)-P(V) regent cn e successfully used for simultneous determintion of metl ions y cpillry electrophoresis. The pre-column complextion of oth metl ions efore the seprtion offers possiility to determine oth ions in single run with good determintion using direct UV detection. The proposed method using Mo(VI) P(V) regent is not only one of the most sensitive nd selective methods for the simultneous determintion of chromium nd vndium, ut lso excellent in terms of ccurcy nd simplicity. It is new pproch nd could e n lterntive to the rpid simultneous determintion of chromium nd vndium in the procedures reported erlier [22,27]. The sensitivity in terms of detection limits nd precision in terms of reltive stndrd devition of the present method re very relile for the determintion of chromium nd vndium in rel smples down to ng g -1 levels in queous medium t room temperture (25 ± 5 o C). Acknowledgements The uthors would like to thnk the Third World Acdemy of Sciences (TWAS) nd Chinese Acdemy of Sciences (CAS) for wrding Visiting Scholr Fellowship to M. J. Ahmed. References 1. G. D. Clyton nd F. E. Clyton (ed), Ptty s Industril Hygiene nd Toxicology, 3 rd ed., Vol. 2A, John Wiley nd Sons, New York (1981) L. S. Hurley in Trce Element Anlyticl Chemistry in Medicine nd Biology, P. Brtter nd P. Schrmel, ed., Vol.2, Wlter de Gruyter, Berlin (1984) A. Mrcov, D. Jirov, H. Jnci nd J. Lener, Science Totl Environ.,Prt 1 (1993) E16/ R. A. Goyer, in: Csrett nd Doull s Toxicology C. D. Klssen (ed.), 6 th ed., McMilln Pulishing Compny, New York (21) 826.

13 Pk. J. Anl. Environ. Chem. Vol. 8, No. 1 & 2 (27) R. J. Shmerger, M. S. Gusch, C. F. Willis, I. J. McCormck, in: Trce Sustnces in Environmentl Helth XII, D. D. Hemphil, University Missouri, Columi (1978). 6. M. M. Key, A. F. Henschel, J. Butter, R. N. Ligo nd I.R. Tershd (eds) Occuptionl Diseses A Guide to Their Recognition, US Deprtment of Helth, Eduction nd Welfre, US Government Printing, Wshington, DC, June (1977). 7. J. R. Pretty, E. A. Bluugh, J. A. Cruso nd T. M. Dvidson, Anl Chem., 66 (1994) S. Hirt, Y. Umezki nd M. Iked, Anl. Chem., 58 (1986) R. R. Greenerg, H. M. Kingstone nd T. M. Sullivn, Fresenius J. Anl. Chem., 332 (1988) Y. Wu nd G. Schwedt, Fresenius J. Anl. Chem., 329 (1987) P. J. Potts, P. C. We, J. S. Wtson nd D. W. Wright, J. Anl. At. Spectrom.,2 (1987) C. M. Dvidson, R. P. Thoms, S. E. McVey, R. Perl, D. Littlejohn nd A. M. Ure, Anl. Chim. Act, 291 (1994) A. D. Altri, J. Chromtogrpy A,856 (1999) F. Lucen-Conde nd L. Prt, Anl. Chim. Act, 16 (1957) S. Himeno, Y. Nkshim nd K. Sno, Anl. Sci., 14 (1998) T. Oski, S. Himeno, A. Sito nd H. Ktno, Electronlysis, 5 (1993) S. Himeno nd N. Ishio, J. Electronl. Chem., 451 (1998) I. Kitzumi, Y. Nkshim nd S. Himeno, J. Chromtogrphy A, 939 (21) L. Krivnkov, P. Pntuckov nd P. Bocek, J. Chromtogrphy A, 838 (1999) R. A. Vercruysse, Hzrdous Metls in Humn Toxicology, Prt B, Elsevier, New York (1984) J. C. Vn Loon nd R. R. Brefoot, Anlyticl Methods for Geochemicl Explortion, Acdemic Press, New York (1989). 22. A. A. Mohmed nd M. F. El-Shht, Anl. Sci., 16 (2) S. Mitr (ed), Smple Preprtion Techniques in Anlyticl Chemistry Wiley Interscience, New Jersey (23) Wter.shtml 25. S. S. Borges, M. Korn nd J. L. F. Costlim, Anl. Sci., 18 (22) M. Jmluddin Ahmed nd Arpn K. Bnerjee, Anlyst, 12 (1995) S. Pozdnikov nd A. Pdrusks, Anlyst, 123 (1998) M. Jmluddin Ahmed is Professor of Anlyticl Chemistry t the University of Chittgong (Bngldesh) since His ctivities re focused on method development for trce nd ultr-trce determintion of toxic elements, seprtion sciences, introduction of micellr system, nutrient nlysis, etc.