*, Masahide Hatakeyama, Thikara Hosino, Paul R. Haddad

Transcription

1 Journl of Chromtogrphy A, 956 (2002) locte/ chrom Rpid ion chromtogrphy of L-scoric cid, nitrite, sulfite, oxlte, iodide nd thiosulfte y isocrtic elution utilizing postcolumn rection with cerium(iv) nd fluorescence detection Ysuyuki Miur *, Mshide Htkeym, Thikr Hosino, Pul R. Hddd, Deprtment of Chemistry, Fculty of Science, Toki University, Hirtsuk, Kngw , Jpn Austrlin Centre for Reserch on Seprtion Science, School of Chemistry, University of Tsmni, GPO Box , Hort 7001, Tsmni, Austrli Astrct Rpid seprtion nd determintion of mixtures of L-scoric cid, nitrite, sulfite, oxlte, iodide nd thiosulfte y conventionl ion chromtogrphy is often difficult due to incomplete seprtion of L-scoric cid nd nitrite from the wter pek when using eluents giving short elution times for iodide nd thiosulfte. Seprtion of the six species within out 15 min hs een chieved y isocrtic elution using resin-sed ion-exchnge column with cronte eluent contining trce mount of 1,3,5-enzenetricroxylic cid (BTA) nd fluorescence mesurement of cerium(iii) formed vi postcolumn rections of the seprted smple species with cerium(iv). Clirtion plots of pek height versus concentrtion were liner up to 10.0 mm (1.76 ppm) for L-scoric cid, 8.0 mm (0.37 ppm) for nitrite, 8.0 mm (0.70 ppm) for oxlte, 80.0 mm (10.2 ppm) for iodide nd 25.0 mm (2.80 ppm) for thiosulfte, whilst the sulfite clirtion ws liner up to 25.0 mm (2.00 ppm) when pek re ws plotted ginst concentrtion. Detection limits (defined s S/N 5 3) were 18 pp for L-scoric cid, 4 pp for nitrite, 16 pp for sulfite, 7 pp for oxlte, 72 pp for iodide nd 37 pp for thiosulfte. The proposed method ws pplied successfully to the determintion of L-scoric cid, nitrite, sulfite, oxlte, iodide or thiosulfte in wter smples Elsevier Science B.V. All rights reserved. Keywords: Detection, LC; Wter nlysis; Derivtiztion, LC; Ascoric cid; Nitrite; Sulfite; Oxlte; Iodide; Thiosulfte; Inorgnic nions; Orgnic cids; Cerium; Benzenetricroxylic cid 1. Introduction retined ions re mixed with more strongly retined species. For exmple, wekly retined species such Ion chromtogrphy (IC) is one of the most s L-scoric cid nd nitrite re difficult to seprte powerful techniques for the determintion of low- from the wter dip when strong eluent is used in moleculr-mss ionic sustnces. However, one diffi- order to resolve strongly retined species such s culty in using conventionl IC rises when poorly iodide nd thiosulfte in resonle time. Severl IC pproches hve een reported for such mixtures, especilly grdient elution hs een employed y *Corresponding uthor. Sunden et l. [1], Trter [2] nd Wty et l. [3] for E-mil ddress: ymiur@keyki.cc.u-toki.c.jp (Y. Miur). mixtures of fluoride, chloride, nitrite, sulfide, iodide / 02/ $ see front mtter 2002 Elsevier Science B.V. All rights reserved. PII: S (01)

2 78 Y. Miur et l. / J. Chromtogr. A 956 (2002) nd thiosulfte. The present uthors hve previously 2. Experimentl estlished rpid nd sensitive seprtions of mixtures contining sulfide, sulfite nd thiosulfte [4], 2.1. Regents L-scoric cid, sulfide, sulfite nd thiosulfte [5] nd sulfide, sulfite, thiocynte nd thiosulfte [6], sed All of the chemicls used were of nlyticlon their postcolumn rections with iodine nd photo- regent grde nd were used without further purificmetric mesurement of the residul iodine. In these tion. The wter used ws distilled twice nd then methods, L-scoric cid nd sulfide were eluted t deionized with Milli-QII instrument (Nippon Milliretention times very similr to wter y using pore, Yonezw, Ymgt, Jpn). An eluent comstrong eluent, ut these nlytes could e detected prising 1.8 mm sodium cronte 1.7 mm sodium ecuse the detection system used eliminted the hydrogencronte 4 mm BTA ws otined y wter dip. Therefore, use of such postcolumn dding 4 ml of 1 mm BTA to mixture of 3.6 ml of rection is incresingly desirle from the viewpoint 0.5 M sodium cronte nd 3.4 ml of 0.5 M sodium of rpid chromtogrphic determintion of mixtures hydrogen cronte, nd diluting it to 1 l with wter. of wekly nd strongly retined species. Wolkoff nd A solution of 0.01 M cerium(iv) sulfte in 2 M Lrose hve used cerium(iv) s postcolumn re- sulfuric cid solution ws prepred y dissolving ction regent for IC detection of polythiontes nd 1.03 g of cerium(iv) sulfte tetrhydrte (Knto thiosulfte [7,8], nd Lee nd Field hve used Chemicl, Tokyo, Jpn) (98%) in wter contining similr system for nitrite, nitrte, thiosulfte nd 28.2 ml of sulfuric cid (95%), nd diluting the iodide, fter preliminry reduction of nitrte to nitrite solution to 250 ml with wter. A postcolumn re- [9]. In the postcolumn rection, cerium(iv) ws ction solution of 0.4 mm cerium(iv) in 0.15 M reduced to cerium(iii) nd the cerium(iii) ws sulfuric cid ws prepred y dding 10 ml of the mesured fluorometoriclly. We hve found tht 0.01 M cerium(iv) solution to 250-ml volumetric cerium(iv) cn lso e converted into cerium(iii) y flsk contining 3.5 ml of 5 M sulfuric cid, nd postcolumn rections with L-scoric cid, sulfite diluting it to the mrk. A stndrd nitrite solution nd oxlte in n cidic medium. Use of cerium(iv) (0.01 M) ws prepred y dissolving g of s postcolumn gent should therefore provide dried sodium nitrite (Wko Pure Chemicl, Osk, rpid, sensitive nd selective method for the de- Jpn) (98.5%) in wter contining 50 ml of M termintion of L-scoric cid, nitrite, sulfite, oxlte, sodium hydroxide s stilizer [10,11] nd diluting iodide nd thiosulfte. to 500 ml with wter. A stndrd solution of oxlte In this study, n IC is proposed for rpid de- (0.05 M) ws otined y dissolving g of termintion of L-scoric cid, nitrite, sulfite, oxlte, sodium oxlte (Wko Pure Chemicl) (99.5%) in iodide nd thiosulfte, sed on isocrtic elution wter, nd diluting it to 500 ml. A stndrd iodide from n ion-exchnge column using cronte solution (0.1 M) ws prepred y dissolving eluent contining trce mount of 1,3,5-enzene- g of potssium iodide (Nkli Tesque, Kyoto, tricroxylic cid (BTA), followed y the fluores- Jpn) (99.5%) in wter contining 100 mg sodium cence mesurement of cerium(iii) formed y post- cronte s stilizer, nd diluting it to 250 ml. column rection with cerium(iv). The optiml con- Solutions of L-scoric cid (out 0.05 M) nd ditions re estlished y vrying the concentrtion sulfite (0.05 M) were otined y dissolving 0.89 g of BTA in the cronte eluent, the mounts of of L-scoric cid (Wko Pure Chemicl) nd 0.52 g cerium(iv) nd sulfuric cid in the postcolumn of sodium hydrogen sulfite (Wko Pure Chemicl), rection solution, the flow-rte of the rection solu- respectively, in 100 ml of oxygen-free wter. A stock tion, the rection temperture nd the length of the thiosulfte solution (out 0.1 M) ws prepred y rection tue. Under the proposed conditions, the six dissolving sodium thiosulfte penthydrte (Nkli smple species re determined within 15 min without Tesque) in wter contining smll mount of use of grdient elution. This method is then pplied sodium cronte (0.01%) s stilizer. These successfully to the nlysis of wter smples. solutions of L-scoric cid, sulfite nd thiosulfte

3 Y. Miur et l. / J. Chromtogr. A 956 (2002) were then stndrdized y iodometric titrtion. Work- smple species reduced the cerium(iv) to produce ing solutions of L-scoric cid, nitrite, sulfite, cerium(iii). Fluorescence of the cerium(iii) ws oxlte, iodide nd thiosulfte were otined y monitored using excittion nd emission wvelengths pproprite dilution of their stndrd solutions. of 256 nd 354 nm, respectively Apprtus 3. Results nd discussion A model LC-10A pump (Shimdzu, Kyoto, Jpn) ws used to pss the eluent through smple 3.1. Effect of BTA in cronte eluent on injection vlve (Rheodyne, Berkeley, CA, USA) resolution using conductivity detection equipped with 300-ml loop, nd then through Dionex Ion Pc AG4A gurd column (5 cm34 mm Initil studies were performed using conductivity I.D.) nd AS4A nlyticl column (25 cm34 mm detection. When 1.8 mm sodium cronte 1.7 I.D.) connected in series. An dditionl pump (Model mm sodium hydrogen cronte solution t flow- DMX-2000, SNK, Tokyo, Jpn) ws used to run the rte of 1.0 ml min ws used s the eluent for postcolumn rection solution through mixing tee to resolution of common nions on Dionex Ion Pc mix with the column effluent. Cerium(III) formed y AG4A nd AS4A columns in series, very long the postcolumn rection etween ech nlyte nd retention times for elution of iodide (34.6 min) nd cerium(iv) in the rection tue ws mesured with thiosulfte (51.4 min) nd excessively rod peks fluorometer (Model RF-10AXL, Shimdzu). Chro- were oserved. Whilst n increse in eluent conmtogrms were otined using Shimdzu Model centrtion could ccelerte the elution of iodide nd U-135 recorder or Shimdzu Model CR6A thiosulfte, it led to incomplete seprtion of L- Chromtopck. scoric cid from the wter pek. Trce mounts of BTA were therefore dded to the cronte hydro Recommended procedure gencronte eluent in view of the high eluotropic strength of the BTA solution [12]. The effects of The columns were equilirted y 1.8 mm dding BTA re shown in Tle 1, from which it cn sodium cronte 1.7 mm sodium hydrogencron- e seen tht whilst n increse in BTA concentrtion te eluent contining 4 mm TBA t flow-rte of 1.0 ccelerted elution of ll nlytes, retention times of ml min, nd then 300-ml liquot of smple oxlte, iodide nd thiosulfte were decresed most solution ws injected. The postcolumn rection solu- significntly. When 4 mm of BTA ws dded to the tion contining 0.4 mm cerium(iv) 0.15 M sulfuric 1.8 mm cronte nd 1.7 mm hydrogencronte cid ws dded to the column effluent t flow-rte eluent, ll six nlytes could e resolved completely 0.3 ml min, nd the rection mixture pssed to within out 15 min, with good pek shpes. At rection tue (2 m30.5 mm I.D.), in which the higher concentrtion (6 mm) of BTA, the L-scoric Tle 1 Effect of concentrtion of BTA in the cronte eluent on retention times of the six nlyte species Concentrtion Elution time (min) of BTA (mm) L-Ascoric cid NO2 SO3 C2O4 I S2O Wter ws eluted t 1.8 min. The eluent contined 1.8 mm sodium cronte nd 1.7 mm sodium hydrogencronte ws used t flow-rte of 1.0 ml min.

4 80 Y. Miur et l. / J. Chromtogr. A 956 (2002) cid pek overlpped prtilly with the nitrite pek, 3.2. Selection of wvelengths for fluorescence nd lso the seprtion of iodide from thiosulfte mesurement of cerium(iii) ecme poorer. Consequently, 1.8 mm cronte 1.7 mm hydrogencronte solution contining 4 Excittion nd emission spectr of cerium(iii) mm BTA ws used s n eluent in this work nd were mesured, in which the cerium(iii) solution chromtogrm otined using this eluent with con- ws prepred y dding 10 ml of 0.6 mm ductivity detection is shown in Fig. 1. An injection cerium(iv) sulfte in 0.15 M sulfuric cid nd 5 ml of the six nlyte species (together with sulfte of 0.1 mm L-scoric cid to 25-ml volumetric which often coexists with sulfite) showed tht L- flsk contining 5 ml of 1.8 mm sodium scoric cid could not e seprted completely from cronte 1.7 mm sodium hydrogencronte 4 the wter dip, nor could sulfite e seprted from mm BTA solution, nd diluting it to the mrk. sulfte. In view of this, fluorescence detection fter Mximum fluorescence intensity of cerium(iii) in postcolumn rections ws utilized in further experi- the solution ws otined t wvelengths of 256 nd ments. 354 nm for excittion nd emission, respectively. These wvelengths were used in ll susequent experiments Optimiztion of the postcolumn rection conditions First, the composition of the postcolumn rection solution ws optimized. The concentrtion of cerium(iv) in the rection solution ws vried over the rnge mm, the concentrtion of sulfuric cid eing held constnt t 0.15 M. Pek heights for the tested nlytes re plotted in Fig. 2, from which it cn e seen tht pek heights for ll nlytes except L-scoric cid reched mximum t 0.4 mm cerium(iv). Next, the effect of sulfuric cid concentrtion in the 0.4 mm cerium(iv) solution ws mesured over the rnge M; Fig. 2 shows tht incresed cidity cused n slight increse in pek heights for nitrite, oxlte, iodide nd thiosulfte, ut decrese for L-scoric cid nd sulfite. A 0.4 mm cerium(iv) in 0.15 M sulfuric cid ws selected s the optimum postcolumn rection solution. The flow-rte of the rection solution ws vried over the rnge ml min nd the results otined re shown in Fig. 3. Pek heights generlly decresed with incresing the flow-rte, ut sulfite, iodide nd thiosulfte showed mximl pek heights t flow-rte of 0.3 ml min. Rection coils Fig. 1. Chromtogrms of the six nlyte species nd sulfte comprising tues (0.5 mm I. D.) of three different otined using suppressed conductivity detection. A 1.8 mm lengths (0.5, 2.0 nd 5.0 m) ws used to find the sodium cronte 1.7 mm sodium hydrogencronte eluent optiml length of tue for the postcolumn rection. contining 4 mm 1,3,5-enzenetricroxylte ws used t flow- The effect of tue length on pek height is listed in rte of 1.0 ml min. Peks: 1510 mm L-scoric cid; 2510 mm nitrite; 3510 mm sulfite; 4510 mm oxlte; 5510 mm Tle 2. A rection tue of 2-m length gve slightly iodide; 6550 mm thiosulfte; 752 mm sulfte. lower pek heights for L-scoric cid, sulfite nd

5 Y. Miur et l. / J. Chromtogr. A 956 (2002) Fig. 2. Effects of concentrtions of () cerium(iv) nd () sulfuric cid in the postcolumn rection solution on pek heights of the nlyte species. () Effect of concentrtion of cerium(iv) in 0.15 M sulfuric cid; () effect of concentrtion of sulfuric cid in 0.4 mm cerium(iv) sulfte solution. Key: 158 mm L-scoric cid; 255 mm nitrite; 3520 mm sulfite; 455 mm oxlte; 5540 mm iodide; 6520 mm thiosulfte. oxlte compred with 0.5-m tue, ut gve lmost sme pek height for ech nlyte except nitrite nd oxlte s 5-m tue. A 2-m rection tue ws therefore used in further studies. The effect of temperture (over the rnge C) of the postcolumn rection on pek height is lso listed in Tle 2. Pek heights for ll nlytes except L- scoric cid showed only minor increse when the temperture ws rised, nd for this reson the postcolumn rection ws crried out t room temperture of round of 8C. A chromtogrm otined under the selected optiml conditions is shown in Fig. 4, from which it cn e seen tht complete resolution ws otined in 15 min with no interference from ny wter dip Anlyticl performnce chrcteristics Fig. 3. Effect of flow-rte of the postcolumn rection solution on pek heights of the nlyte species. Key: 158 mm L-scoric cid; 255 mm nitrite; 3520 mm sulfite; 455 mm oxlte; 5540 mm iodide; 6520 mm thiosulfte. Clirtion plots were constructed using 300-ml liquots of smple solutions contining L-scoric cid, nitrite, sulfite, oxlte, iodide nd thiosulfte, seprted under the conditions descried in Section 2.3. Clirtion grphs sed on pek height, for ll nlyte species except sulfite, were liner up to 10 mm (1.76 ppm) for L-scoric cid, 8 mm (0.37 ppm) for nitrite, 8 mm (0.70 ppm) for oxlte, 80 mm

6 82 Y. Miur et l. / J. Chromtogr. A 956 (2002) Tle 2 Effects of rection coil tuing length nd temperture on the postcolumn rection Prmeter Pek height (cm) 2 2 L-Ascoric cid NO2 SO3 C2O4 I S2O3 (6 mm) (6 mm) (25 mm) (4 mm) (20 mm) (15 mm) Tue length (m) Temperture (8C) Temperture ws djusted to 8C. A 2-m tue ws used. Tle 3 Precision of the proposed method nd detection limits Species Precision Detection limit t S/N53 Men vlue SD RSD (pp) (ppm) (ppm) (%) L-Ascoric cid NO SO C O I S O The precision ws estimted from five replicte results otined for mixture contining ppm L-scoric cid, ppm nitrite, 1.60 ppm sulfite, ppm oxlte, 2.54 ppm iodide nd 1.12 ppm thiosulfte; SD, stndrd devition; RSD, reltive stndrd devition. Tle 4 Determintions of L-scoric cid in soft drinks nd nitrite in river wter Smple Proposed method PCR UV detection Content in originl Added Found Recoveries Content in originl smple (ppm) (ppm) (ppm) (%) smple (ppm) c L-Ascoric cid in soft drinks A B d Nitrite in river wter C Excess iodine fter postcolumn rection with L-scoric cid in the column effluent ws mesured photometriclly [4]; PCR, postcolumn rection. Men from three replicte results. c Dilutions to 400 times the originl volume with wter were used. d Dilutions to four times the originl volume with wter were used.

7 Y. Miur et l. / J. Chromtogr. A 956 (2002) (10.2 ppm) for iodide, nd 25 mm (2.80 ppm) for Cu, Fe nd Fe gve smll negtive peks t thiosulfte. When pek re ws plotted ginst elution time close to L-scoric cid. But these concentrtion the clirtion plot for sulfite ws ctions in mounts of 1 mm could e eliminted liner up to 25.0 mm (1.20 ppm). In ll cses, with the ction-exchnge column (50 mm34.0 mm correltion coefficients of more thn were I.D.) pcked with Amerlite IR-120 resin ( otined. The precision of this method nd the mesh) in the N form. Anions of IO 3, BrO3 nd detection limits of nlyte species re shown in S were eluted t retention times close to L-scoric Tle 3. cid, nd mlete ws eluted t time close to Interference effects y vrious foreign ions on the sulfite, ut these foreign ions when present t 0.1 determintion of the nlytes were investigted. Ions mm did not interfere with the determintion of L- 2 2 such s Cl, Br, SO 4, HPO 4, formte, propion- scoric cid nd sulfite. te, cette, lctte, n-utyrte, citrte, trtrte, mlo nte, succinte, NH 4, N, K, Mg, C, Zn, 31 Co, nd Al gve no chromtogrphic peks t 2 concentrtions s high s 1 mm. NO3 t 1 mm cused negtive pek etween nitrite nd sulfite peks, ut it did not gve ny interference with the determintions of nitrite nd sulfite. Ech ction of Fig. 4. Chromtogrms of L-scoric cid, nitrite, sulfite, oxlte, iodide nd thiosulfte with postcolumn fluorescence detection. Peks: 158 mm L-scoric cid; 255 mm nitrite; 3520 mm sulfite; 455 mm oxlte; 5540 mm iodide; 6520 mm thiosulfte. Fig. 5. Chromtogrms of nlyte species in wter smples. () L-scoric cid in soft drink; () nitrite in river wter; (c) sulfite, oxlte nd thiosulfte in groundwter. Peks: 15L-scoric cid; 25nitrite; 35sulfite; 45oxlte; 55thiosulfte.

8 84 Y. Miur et l. / J. Chromtogr. A 956 (2002) Tle 5 Determintion of sulfite, oxlte nd thiosulfte in groundwter Anlyte Proposed method PCR UV detection Content in originl Content in originl Added,c Found,c Recovery c smple (ppm) smple (ppm) (ppm) (ppm) (%) SO C O S O Excess iodine fter postcolumn rections with L-scoric cid in the column effluent ws mesured photometriclly [4]; PCR, postcolumn rection. Smples diluted to 2 times the originl volume with wter were used. c Men from three replicte results Appliction to the nlysis of wter smples References The proposed method ws pplied to the de- [1] T. Sunden, M. Lindgren, A. Cedergren, D.D. Siemer, Anl. termintion of the six nlyte species in wter Chem. 55 (1983) 2. [2] J.G. Trter, Anl. Chem. 56 (1984) smples (soft drink, river wter nd groundwter). [3] T. Wty, K. Hykw, K. Nomur, M. Miyzki, Bunseki Tle 4 lists the results for the determintion of Kgku 43 (1994) 817. L-scoric cid in soft drinks nd for the determi- [4] Y. Miur, M. Tsumoto, T. Koh, Anl. Sci. 10 (1994) 545. ntion of nitrite in river wter, nd Tle 5 the [5] Y. Miur, T. Mruym, T. Koh, Anl. Sci. 11 (1995) 617. results for the determintion of sulfite, oxlte nd [6] Y. Miur, K. Fuksw, T. Koh, J. Chromtogr. A 804 (1998) 143. thiosulfte in groundwter. Fig. 5 shows chromto- [7] A.W. Wolkoff, R.H. Lrose, Anl. Chem. 47 (1975) grms otined for these wter smples. These [8] A.W. Wolkoff, R.H. Lrose, J. Chromtogr. Sci. 14 (1978) results show tht the proposed method could e 353. pplied successfully to the rpid determintion of the [9] S.H. Lee, L.R. Field, Anl. Chem. 56 (1984) [10] T. Nomur, G. Nkgw, Nippon Kgku Kishi 1978 six nlytes in treted nd nturl wter smples (1978) without the need for grdient elution or smple [11] A.A. Ensfi, M. Smimifr, Tlnt 40 (1993) pretretment. [12] Y. Miur, J.S. Fritz, J. Chromtogr. 482 (1989) 155.