Research Article Determination of Chlorinity of Water without the Use of Chromate Indicator

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1 Interntionl Anlyticl Chemistry Volume 21, Article ID 299, pges doi:1.1155/21/299 Reserch Article Determintion of Chlorinity of Wter without the Use of Chromte Indictor Te-Kee Hong, 1 Myung-Hoon Kim, 2 nd Myung-Zoon Cze 1 Deprtment of Chemistry, Hnseo University, Seosn, Choongnm 19-, Repulic of Kore 2 Deprtment of Sciences, Georgi Perimeter College, Dunwoody, GA, USA Deprtment of Chemistry, Hnyng University, Seoul 1-91, Repulic of Kore Correspondence should e ddressed to Myung-Hoon Kim, myung.kim@gpc.edu Received 2 August 21; Revised 1 Novemer 21; Accepted Decemer 21 Acdemic Editor: John P. Hrt Copyright 21 Te-Kee Hong et l. This is n open ccess rticle distriuted under the Cretive Commons Attriution License, which permits unrestricted use, distriution, nd reproduction in ny medium, provided the originl work is properly cited. A new method for determining chlorinity of wter ws developed in order to improve the old method y lleviting the environmentl prolems ssocited with the toxic chromte. The method utilizes meditor, wek cid tht cn form n insolule slt with the titrnt. The meditor triggers sudden chnge in t n equivlence point in titrtion. Thus, the equivlence point cn e determined either potentiometriclly (using meter) or simply with n cid-se indictor. Three nontoxic meditors (phosphte, EDTA, nd sulfite) were tested, nd optiml conditions for the shrpest chnges were sought. A comintion of phosphte ( meditor) nd phenolphthlein (n indictor) ws found to e the most successful. The choices of the initil nd the concentrtion of the meditor re criticl in this pproch. The optimum concentrtion of the meditor is c. 1 2mM,nd the optimum vlue of the initil is c. 9 for phosphte/phenolphthlein system. The method ws pplied to smple of se wter, nd the results re compred with those from the conventionl Mohr-Knudsen method. The new method yielded chlorinity of smple of se wter of (1.5 ±.22) g/kg, which is out 2.5% higher thn the vlue (1.12 ±.22) g/kg from the old method. 1. Introduction Chlorinity is one of the most fundmentl quntities ssocited with wter qulity [1, 2], nd it is directly relted to the slinity of se wter [] nd often used to determine the slinity []. In recent yers, physicl methods of determining slinity [5, ], such s coulometry, mesurements of conductivity, refrctive index, or density, hve ecome more populr ecuse of their speed. Nevertheless, chemicl mesurements of chlorinity still remins n importnt nd independent method of chrcterizing wter qulity. Vrious chemicl methods hve een reported for chlorinity determintion: the grvimetric method with AgCl precipittes [ 9], vrious volumetric precipittion titrtions with silver (I) or mercury (II) ions [ 9], nd recent spectroscopic method utilizing the Rmn scttering nd of OH stretching of wter [1]. Among these chemicl methods, the volumetric titrtions with precipittion with Ag + hve een most populr ecuse it is less time consuming thn the grvimetry. Severl different wys of determining the equivlence point hve een reported for the volumetric titrtions with silver ion, such s () use of vrious visul indictors [11, 12], () thermometric titrtion mesuring enthlpy chnges [1], nd (c) potentiometric titrtion [1]. The nlyticl methods recommended in the Stndrd Method for the Exmintion of Wter nd Wste Wter [15] nd the Officil nd Stndrdized Method of Anlysis [1] re: (1) rgentometric titrtion with silver nitrte using potssium chromte indictor, (2) titrtion with mercuric nitrte using s-diphenylcrzone indictor, nd () potentiometric titrtion using glss nd silver-silver chloride electrode. The present work is imed t improving the common volumetric method (1) of rgentometric titrtion. However, the rgentometry with the Mohr or Mohr-Knudsen method [1, 5, ], which is sed on ppernce of the red color of silver chromte precipitte t the equivlence point

2 2 Interntionl Anlyticl Chemistry 5 c d 5 c d 5 AgNO (ml) () 5 AgNO (ml) () Figure 1: () Titrtion curves for 25. ml of.1 M NCl with.5 M AgNO in the presence of 1. mm phosphte t vrious strting vlues: ().9, ()., (c)., nd (d) 5.1. () Titrtion curves for 25. ml of.1 M NCl with.5 M AgNO in the presence of vrious phosphte concentrtions: ().5, ().2, (c) 2., nd (d). mm. rises concerns with environment prolems ecuse of the toxicity of the chromte with hexvlent chromium. Although trivlent chromium, Cr(III), is nontoxic, the cute nd chronic toxicity nd crcinogenicity of the hexvlent chromium, Cr(VI), hve een well documented [1 19]. Thus, conversion of Cr(VI) to Cr(III) nd specition nd fte of chromium in the environment nd in model systems nd kinetics of reduction of Cr(VI) hve drwn much interest in recent yers [2 25]. Chromium pollution in surfce wter is lrgely due to dischrge from chemicl plnts where chromium is used in tnning lether, s mordnt in the textile industry, nd in the glvnic process for nodizing luminum in the ircrft industry nd other industries. The current Mximum Contminnt Level (MCL) of chromium from the EPA (USA) is 1 pp (for wter), nd the Permissile Exposure Limit (PEL) from the OSHA (USA) is 52 µg/m (for ir). The ltter is much higher thn new proposed level of 1 µg/m [2]. Thus, it is desirle to reduce chromium dischrge to environment in ll possile wys. The toxicity of mercury is lso well known [1]: thus, the method (2) is not desirle one. With this in mind, we developed n environmentlly more enign method for determining the chlorinity of wter without using the hexvlent chromium or divlent mercury slt. Chnges in during certin types of precipittion titrtions hve long een oserved [12, 2, 2], nd the chnge cn e mde lrge enough so tht n equivlence point cn e determined either potentiometriclly with electrode or using cid-se indictors under suitle conditions. When rections involve hydrolysis of ction or n nion yielding lrge, n equivlence point cn e detected potentiometriclly [29 1]. A quntittive model to predict the chnge in such hydrolytic systems hve een reported [2, ]: Docnik nd coworkers proposed mthemticl model for the titrtion of metl ion (P 2+ ) with oxlte nd other nions []. In their studies, fter ll of the led is removed s led oxlte precipittes t the equivlence point, the excess oxlte nions pick up H + from solution to form oxlic cid: this triggers rpid increse in. The equivlence point ws determined to e crossing point (i.e., the point t which two tngents on the two erlier sections of the titrtion curve intersect) [2 ]. Thus, the theory nd prctice of hydrolytic types of precipittion rection hve een estlished. A theory nd prctice for the precipittion titrtion tht does not involve hydrolysis, however, hve not een well studied yet except in our recent report [5]. The rgentometric titrtion of chloride per se does not involve hydrolysis of n nion or ction ecuse neither Ag + nor Cl hydrolyses. Thus, very little chnge in (Δ <.1) hs een oserved round n equivlence point during titrtion of chloride ion with silver ion [2]. In the presence of vrious dsorption indictors, however, somewht lrger chnges in hve een oserved [12, 2]; typiclly, Δ is less thn three units. This chnge is not lrge enough for n cid-se indictor to respond shrply t the equivlence point lthough it cn e followed potentiometriclly with meter []. In our recent work [5], we hve fully demonstrte, oth in theory nd prctice, tht the chnge t the equivlence point cnemdesufficiently lrge even though the precipittion rection does not involve hydrolysis. This ws possile y introducing n dditionl regent (chromte, meditor) tht undergoes hydrolysis so tht the concentrtion of H + cn e chnged drsticlly t the equivlence point. Equivlence points were detected with meter, which yielded less thn 1% of reltive errors tht depend on the meditors [5]. For clrity, rief comprison with the old Mohr method nd current new method is presented elow in terms of the rection involved Comprison of the Current Approch with the Mohr Method. The Mohr method utilizes the formtion of red-colored precipitte of titrnt (Ag + ) with n indictor (CrO 2 )(see(2)) fter ll thechloride is precipitted out of

3 Interntionl Anlyticl Chemistry c 5 5 d 5 AgNO (ml) () 5 AgNO (ml) c d () Figure 2: () Potentiometric titrtion curves for 25. ml of.1 M NCl with.5 M AgNO in the presence of.2 mm EDTA t vrious strting vlues: ().1, ()., (c)., nd (d) 5.. () Titrtion curves for 25. ml of.1 M NCl with.5 M AgNO t vrious concentrtions of EDTA: ()., ().2, (c)., nd (d) 1.2 mm. the solution y Ag + (see (1)) t the equivlence point Cl +Ag + AgCl(s) (white) Anlyte rection (1) 2 CrO ( yellow ) +2Ag + Ag 2 CrO (s) (red) (2) Indictor rection The ppernce of the red precipitte of silver chromte signls the end point of the titrtion. This method hs een prticulrly useful in the determintion of chlorinity [1,, ] in smples of se wter. In the current method [5], wekcid(ha)whose conjugte se (A ) cn form slightly solule slt (AgA) with the titrnt (Ag + ) is dded in plce of the visul indictor (chromte) ove; this llows equivlence point to e detected either with electrode [5] or with n cid-se indictor. The cid (HA) or its conjugte se (A )ctss meditor (or s n indictor) so tht HA cn relese H + when the equivlent point is reched. This system presents n equilirium prolem in which n cid-se rection is coupled to two soluility equiliri, resulting in four coupled equiliri including the ioniztion of wter (see ()) Cl +Ag + AgCl(s) (white) K sp = [ Ag +][ Cl ], () HA H + +A [ H + ][ A ] K =, [HA] () A +Ag + AgA(s) K sp = [ Ag +][ A ], (5) H 2 O H + +OH K w = [ H +][ OH ]. () If the soluility of AgCl is less thn tht of AgA, AgCl will e precipitted out first. After ll the Cl is removed, then dditionl Ag + will rect with A to remove it s precipitte (AgA). As A is eing removed, HA must dissocite to replenish A, therey generting H +. Therefore, the of the system decreses t the equivlence point [5]. In this present work, we serched for the est nontoxic meditor nd the est conditions tht cn ring lrger nd shrper chnge so tht even common cid-se indictor cn e employed in detecting n equivlence point for the titrtion. It is demonstrted tht equivlence point is determined y using nontoxic meditor (phosphte) nd n cid-se indictor(phenolphthlein) without using meter. This new pproch is successfully pplied for determintion of chlorinity of smple of se wter. 2. Experimentl 2.1. Regent nd Apprtus. All chemicls used were nlyticl regent grde nd were used without further purifiction. All solutions were prepred with deionized wter. AgNO solutions were stndrdized using the Mohr method [ 9]. vlues were mesured with Fisher Accumet Selective Ion Anlyzer Model 5 Meter nd n Orion Model 1 Digitl Meter. Glss electrodes of Orion Model-91 series nd similr type of comintion electrodes were used for the mesurements. Initil s were djusted y dding.1 M NOH or.1 M HCl. Solutions were stirred mgneticlly during titrtion.. Results nd Discussion Figure 1() presents titrtion curves for 25. ml of.1 M NCl with.5 M AgNO in the presence of meditor (1. mm phosphte) t vrious vlues of.9,.,., nd 5.1. As predicted from the theory, the curves hve sme pttern s Figure () in [5]. At the highest initil vlues, the chnge in is the most with.9 units, nd t the lowest initil, the chnge is the smllest with 1. units. The chnges re summrized in Tle 1. The crossing points for ll the curves occurred somewht erlier thn the equivlence point. Figure 1() presents titrtion curves for the sme solutions t vrious phosphte concentrtions (.5,.2, 2.,

4 Interntionl Anlyticl Chemistry M AgNO dded (ml) M AgNO dded (ml) 5 () () Figure : () Titrtion curves of. ml of.1 M NCl with.1 M AgNO solution t two different isulfite concentrtions: ().5 mm (, initil.2), () 5. mm (, initil.). () Titrtion curves of. ml of.1 M NCl with.1 M AgNO solution in the presence of 5. mm isulfite t two different initil vlues: ().12 ( ), (). ( ). Tle 1: Chnge in t vrious vlues of initil with N 2 HPO. Initil rnge Δ Tle 2: Chnge in t vrious concentrtions of N 2 HPO. Concentrtion (mm) rnge Δ nd. mm). Agin, the pttern resemles those predicted from the theory [5]. The crossing points for ll the curves occur very close to the equivlence points. At lower meditor concentrtion, the chnge in is less (Δ = 2.5 with curve ()), nd t higher meditor concentrtion the chnge is the lrgest (Δ =. with curve (d)). Tle 2 summrize the chnge t vrious concentrtion of the meditor. Figure 2() presents titrtion curves for the sme solutions with nother meditor,.2 mm EDTA, t vrious strting vlues: ().1, ()., (c)., nd (d) 5.. Although it exhiits the generl trend, there re reks in the curves. At the higher (.1 nd.), HY is dominnt, nd t the lower (5. nd.), H 2 Y 2 is dominnt t the eginning. The one egun t.1 yielded the lrgest chnge. The nrrow middle plteu for the curves () (d), where the chnge ecomes grdul gin, is ttriuted to the conversion of either HY to H 2 Y 2 or H 2 Y 2 to H Y. The crossing point occurred t out. ml, which is out %errorfromtheequivlencepoint.thus,inthecseof EDTA; however, the inflection points t out.9 ml pper to e etter equivlence point (with 2% of error) thn the crossing point. Figure 2() presents titrtion curves for the sme solutions t vrious EDTA concentrtions rnging from. (). mm (d). The one with the highest concentrtion (. mm) yielded the lrgest chnge. The crossing point for ll curves hs n error of %. Thus, s in Figure 2(), the inflection point ppers to e etter equivlence point thn the crossing points. Thus, EDTA does pper to e good meditor in determining n equivlent point with the crossing point method. All the previous experiments were performed s rther crude qulittive pilot runs using.5 M AgNO. However, the following titrtions (Figures nd ) reimed t otining more ccurte quntittive results y using.1 M AgNO insted of.5 M AgNO, nd y incresing volumes of titrnd (Cl ) from 25. ml to. ml. Typicl titrtion curves of. ml of.1 M NCl with.1 M AgNO solution in the presence of NHSO (the meditor) re presented in Figure () t two different concentrtions of isulfite: ().5 mm (, initil of.2) nd () 5. mm (, initil of.). The two results from the two concentrtions re very different. The one otined t 5. mm isulfite generted curve with well-defined equivlence point. Menwhile, the one with isulfite concentrtion of.5 mm generted grdul chnge from the eginning without ny rek in chnges, thus filing to produce mesurle crossing point. This illustrtes the importnce of controlling the concentrtion of the meditor nd initil vlues. At the lower meditor concentrtion (.5 mm), most of the isulfite exists in the fully deprotonted form (SO 2 )ttheof.2. Therefore, consumption of the sulfite y Ag + cnnot drive rection (HSO H + +SO 2 ) to relese much H +. Similr results of grdul chnge t the equivlence point, without ny shrp rek, were oserved when NCN ws used s meditor. Figure () showstitrtionsinthepresenceof5.mm isulfite t two different initil vlues (().12, nd

5 Interntionl Anlyticl Chemistry 5 1 Tle : Errors in determining equivlence point: volume (ml) of Ag + required using N 2 HPO..2. Tril Meditor (mm) Initil. Crossing Point Inflection Point Averge of Rel. Error.1 % % M AgNO dded (ml) Figure : Titrtion curves of. ml of.1 M NCl with.1 M AgNO solution in the presence of 2.5 mm N 2 HPO t two different initil vlues: ().2 ( ) nd().( ). ().). Both yielded comprly good crossing points. A suitle rnge of initil vlues lies round nd. When severl mm of NHSO re dded, s meditor, the initil of the solution will e in the right rnge, thus djustment of t the eginning is not necessry. However, when H 2 SO is dded s meditor, it will e cidic ( 2) t the eginning; hence, smll mount of se (.1 M NOH) must e dded to rech the optimum rnge. If N 2 SO is used, the solution will e lkline ( 9); therefore, n cid solution (.1 M HNO ) should e dded to ring vlue of the lkline solution down to rnge of. Optimum concentrtion of the meditor ws found to e in the rnge of 2 5 mm: lower concentrtion of the meditor genertes smll nd grdul chnge in, while higher concentrtion will generte less shrp chnges in t the end point yielding lrger error. It is not cler why the increses gin fter equivlence point (fter 1 ml). Figure shows titrtion curves of. ml of.1 M NCl with.1 M AgNO solution in the presence of 2.5 mm N 2 HPO t two different initil vlues: ().2 ( ) nd (). ( ). Even though the titrtion with the higher initil yielded lrger nd shrper chnge, oth results were comprly good. Tle presents results with phosphte t severl different conditions. The crossing point method yielded much etter results (n verge of.1% reltive error) thn the inflection methods. Finlly, we pplied the present method with n cidse indictor to determine the chlorinity of smple of se wter, nd we compred the results of this method with the results from the Mohr-Knudsen Method. The phosphte ws dopted s meditor; phenolphthlein ws employed s visul indictor. The results re summrized in Tle. Five trils were mde; the verge nd stndrd devition vlues were (1.12 ±.22 ) g/kg from the Mohr-Knudsen method nd (1.5 ±.21 9 ) g/kg from the present method. The verge chlorinity from the meditor method ws out 2.5% higher thn tht from the conventionl method; the 5 Tle : Comprison of the Results of Determintion of Chlorinity (g/kg) from the Mohr-Knudsen Method nd the Present Methods with Phosphte/Phenolphthlein s Indictor. Tril Mohr-Knudsen Method Phosphte/Ph pht Method (Present) Difference Ave. ± Std.Dev ± ±.22 precision is out the sme for oth methods. The F- test nd t-test yielded F =.9559 (<.9), t =.1, respectively, suggesting tht the two stndrd devitions do not differ, ut the results (chlorinities) re different somewht (2.5%). The higher vlue oserved with the new method my e explined from the fct tht the new method involves equilirium (2), insted of equilirium (1) in the old method: the dditionl equilirium rection my hve required more Ag + for complete shift of the equilirium rection to the right. Both vlues of the chlorinity of the smple (collected t the Western Se of South Kore) re out 1% lower thn tht of n verge chlorinity of se wter which is 19 g/kg [, 9] tht depends on loction of smpling.. Summry A new method for determining chlorinity of wter without using the chromte indictor ws developed nd successfully pplied to determine chlorinity of se wter. Among the meditors tested, the phosphte in comintion with phenolphthlein yielded the est result. Concentrtion of meditor nd the initil of the solution found to e criticl for the success. Higher meditor concentrtions yielded less ccurte results even though they gve lrger chnges in. At lower meditor concentrtion, the end point is more ccurte, ut chnge is not lrge enough for the visul indictor to ring shrp color chnge. Thus, optimum concentrtion of the phosphte meditor ppers

6 Interntionl Anlyticl Chemistry to e in rnge of 1 2 mm. The of the nlyte solution must e djusted initilly to the lkline side (.5 or higher) so tht phenolphthlein imprts pink color t the eginning of the titrtion. Chlorinity of smple of se wter from this method found to e (1.5 ±.22) g/kg, which is out 2.5% higher thn tht (1.12 ±.22) g/kg from the conventionl Mohr-Knudsen method. This new method my replce the rgentometric titrtion with chromte indictor in the stndrd method [15] of determining chloride in wter nd wste wter. Acknowledgments A grnt from the Writer s Institute (GPC) is much pprecited. The uthors thnk Mureen Burkrt for correcting nd editing the pper. References [1] D.F.Mrtin, Mrinechemistry, inanlyticl Methods, vol. 1, p. 5, Mrcell Dekker, New York, NY, USA, 19. [2] A. H. Brownlow, Geochemistry, Prentice-Hll, Englewood Cliff, NJ, USA, 199. [] T. R. S. Wilson, Slinity nd mjor elements of se wter, in Chemicl Ocenogrphy, J.P.RileyndG.Skirrow,Eds., chpter,acdemicpress,newyork,ny,usa,2ndedition, 195. [] R.A.Cox, Thephysiclpropertiesofsewter, inchemicl Ocenogrphy, J.P.RileyndG.Skirrow,Eds.,vol.1,chpter, Acdemic Press, London, UK, 195. [5] K. Grsshoff, Determintion of slinity, in Methods of Se Wter Anlysis,K.Grsshoff, M. Ehrhrdt, nd K. Kremling, Eds., p. 1, Wiley-VCH, Weinheim, Germny, 19. [] F.MillerondM.L.Sohn,Chemicl Ocenogrphy, chpter2, CRC Press, Boc Rton, Fl, USA, 199. [] I. M. Kolthoff nd E. B. Sndell, Textook of Quntittive Inorgnic Anlysis, McMilln, New York, NY, USA, 199. [] D. C. Hrris, Quntittive Chemicl Anlysis, W.H.Freemn & Co., New York, NY, USA, 192. [9] R. A. Dy nd A. L. Underwood, Quntittive Anlysis, Prentice Hll, New York, NY, USA, 5th edition, 19. [1]J.Duessy,T.Lhomme,M.C.Boiron,ndF.Rull, Determintion of chlorinity in queous fluids using Rmn spectroscopy of the stretching nd of wter t room temperture: ppliction to fluid inclusions, Applied Spectroscopy, vol. 5, no. 1, pp. 99 1, 22. [11] H. A. Litenen, Chemicl Anlysis, chpter 12-1, McGrw Hill, New York, NY, USA, 19. [12] E. Pungor nd E. Schulek, Adsorption indictors, in Indictors, E.Bishop,Ed.,chpter,PergmonPress,Oxford,UK, 192. [1] F.J.Millero,S.R.Schrger,ndL.D.Hnsen, Thermometric titrtion nlysis of sewter for chlorinity, sulfte nd lklinity, Limnology nd Ocenogrphy, vol. 19, pp , 19. [1] D. Jgner, Potentiometric titrtions, in Mrine Electrochemistry, M.WhitfieldndD.Jgner,Eds.,chpter,JohnWiley & Sons, Chishester, UK, 191. [15] L. S. Clesceri, A. E. Greenerg, nd A. D. Eton, Stndrd Methods for the Exmintion of Wter nd Wstewter, Americn Pulic Helth Assocition, Americ Wter Works Assocition, Wter Environment Federtion, Wshington, DC, USA, 29th edition, 199. [1] Officil nd stndrdized method of nlysis, in Anlyticl Methods Committee, C. A. Wtson, Ed., p. 55, Royl Society of Chemistry, Cmridge, UK, 199. [1] Committee on Biologicl Effects of Atmospheric Pollutnts, Chromium: Medicl nd Biologicl Effects of Environmentl Pollutnts, Ntionl Acdemy of Science, Wshington, DC, USA, 19. [1] R. A. Goyer, Toxic effects of metls, in Csrett nd Doul s Toxicology,C.D.Klssen,M.O.Amdur,ndJ.Doull,Eds., pp. 52 5, Mcmillin, New York, NY, USA, rd edition, 19. [19] R. A. Anderson, Essentility of chromium in humns, Science of the Totl Environment, vol., no. 1-2, pp. 5 1, 199. [2] J.M.Eckert,J.J.Stewrt,T.D.Wite,R.Szymczk,ndK.L. Willims, Reduction of chromium(vi) t su-µgl 1 levels y fulvic cid, Anlytic Chimic Act, vol. 2, no. 2, pp. 5 2, 199. [21] F. C. Richrd nd A. C. M. Bourg, Aqueous geochemistry of chromium: review, Wter Reserch, vol. 25, no., pp. 1, [22] B. Deng nd A. T. Stone, Surfce-ctlyzed chromium(vi) reduction: rectivity comprisons of different orgnic reductnts nd different oxide surfces, Environmentl Science nd Technology, vol., no., pp. 2 29, 199. [2] C.-J. Lin, The chemicl trnsformtions of chromium in nturl wters model study, Wter, Air, nd Soil Pollution, vol. 19, no. 1, pp. 1 15, 22. [2] M. Pettine, L. D Ottone, L. Cmpnell, F. J. Millero, nd R. Pssino, The reduction of chromium (VI) y iron (II) in queous solutions, Geochimic et Cosmochimic Act, vol. 2, no. 9, pp , 199. [25] M. Pettine, D. Tonnin, nd F. J. Millero, Chromium(VI) reduction y sulphur(iv) in queous solutions, Mrine Chemistry, vol. 99, no. 1, pp. 1 1, 2. [2] D. Michels, C. Monforton, nd P. Lurie, Selected science: n industry cmpign to undermine n OSHA hexvlent chromium stndrd, Environmentl Helth, vol. 5, rticle no. 5, p., 2. [2] M.-Z. Cze, The dsorption of hydrogen nd hydroxyl ions during precipittion tritrtion, the Koren Chemicl Society, vol. 1, no. 1, p. 1, 19. [2] L. Legrdi, Az dszorpcios indikcio mechnizmus, Mgyr Kemii Folyoirt, vol., no. 1, pp., 19 (Hungrin). [29] N. Hot, Use of meter for indicting the end point of the precipittion titrtion of sulfte with mixed solution of rium nitrte nd led nitrte, Bunseki Kgku, vol. 19, p., 19. [] N. Hot, Use of meter for indicting the end point of the precipitometry. II. Titrtion of hlides, iodte, chromte, nd secondry phosphte, Bunseki Kgku, vol. 2, p. 522, 191. [1] N. Hot, meter for indicting the end point of vrious titrtions in mixed solvent. Precipitometry using titrnt of silver nitrte, led nitrte, sodium sulfide nd neutrliztion titrtion of mmonium compounds, Bunseki Kgku, vol.21, p. 1, 192. [2] D. Dočnik nd D. Brodnjk-Vončin, Hydrolytic potentiometric titrtion of sulphte with ppliction in the nlysis of wters, Anlytic Chimic Act, vol. 1, pp , 195. [] D. Dočnik nd J. Giicr, Vestnik Slovenskeg Kemijskeg Drustv, vol., p. 5, 19.

7 Interntionl Anlyticl Chemistry [] D. Brodnjk Voncin, D. Docnik, nd G. Gomiscek, Hydrolytic precipittion titrtions followed y glss electrode, Anlytic Chimic Act, vol. 2, no. 1-2, pp. 1 15, [5] T.-K.Hong,B.-H.Koo,M.-H.Kim,ndM.-Z.Cze, Useof electrode for precipittion titrtion nlysis: theory nd prctice, Anlyticl Chemistry, vol., p. 115, 29. [] J. F. Coetzee, Precipittion equiliri nd titrtions in queous nd non-queous medi, in Tretise on Anlyticl Chemistry,I.M.Kolthoff nd P. J. Elving, Eds., vol., pp., John Wiley & Sons, New York, NY, USA, 19. [] J. P. Riley, in Chemicl Ocenogrphy,J.P.RileyndG.Skirrow, Eds., chpter 21, Acdemic Press, New York, NY, USA, 195. [] R. A. Berner, Activity coefficients of icronte, cronte nd clcium ions in se wter, Geochimic et Cosmochimic Act, vol. 29, no., pp. 9 95, 195. [9] G. S. Sodhi, Fundmentl Concepts of Environmentl Chemistry, Alph Science Interntionl, 2.

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