Bapanaiah, K. V.

Kannarao, P.

Muralikrishna, U.

Prasad, N. S. N.

English

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The reverse titrations, i.e. tit rations of sodiumthiosulphate, arsenic(III) , ascorbic acid and hydra-zine with iodine, can be carried out using O'INand O'OIN solutions under the same conditions asin the direct titrations and the colour changes atthe end points are just the reverse of those observedin the direct titrations. In the reverse titrationsno blank correction is necessary in titrations ofO·IN solutions, but while titrating with O·OINsolutions, a blank correction of 0·04-0·06 ml O·OINiodine has to be applied for 0·2 ml of 0·01% indicatorsolution added.While titrating with O'OIN solutions, the amountof the indicator added should be 0'1-0'3 ml; whenhigher amounts of indicator solution are employed,the colour changes at the end points are not quitesatisfactory.With a view to applying the method nowdeveloped for the titrimetric determination of as-corbic acid in commercial vitamin C tablets, wehave studied the interferences of some substances.The results indicate that citric, tartaric, oxalic,succinic, malic, maleic and mandelic acids, dex-trose, lactose, mannitol, Ca2+, Mn2+, and Mg2+ donot interfere, whereas Fez+, Ba2+, Li", and Pb2+interfere.The ascorbic acid content in the commercialvitamin C tablets was determined as follows: Thetablet was dissolved in deionized water, and thesolution filtered through a G4 sintered glass crucible.The filtrate was made up to 100 ml and an aliquotof this solution titrated aganist 0'1N iodine solution,using anyone of the five dyes as indicator. A similaraliquot was titrated following the literature method.The results presented in Table 2 show that they arein excellent agreement with those obtained by the,official method.In their studies on the use of neutral red asindicator in the argentometric titration of bromideand iodide, Sierra and Asensit'' stated that thecolour change at the end point is due to the formationof a compound between iodine and neutral red.Since the dyes of the present investigation havealmost .similar structures as neutral red, we believethat a compound is formed between iodine and thedye, and at the end point, thiosulphate, arsenic (III),hydrazine and ascorbic acid react with the com-pound and. regenerate the dye.TABLE 2 - DETERMINATION OF ASCORBIC ACID INCOMMERCIALVITAMIN C TABLETSTrade name Amount of ascorbic acidfound (mg)Manu-facturerBP method* Presentmethod"RedoxonCelinSukceeChewceeRocheGlaxoIDPLLederle461·9+0'3498·6±0·5502-3±0·4480'3±{H461-5±0-4497·6±0·4501'9±O'3 '480'7±0'3*British Pharmacopoeia, 1973, 36.N.OTE,SWe .are grateful to the (SIR, New DeU;I, forthe award of a Junior Resea~ch Fello~ship to:K.M.M.K.P. 'References1. ERDEY, L., BODOR, E. & PAPAY, M., Acta chim. Hung., 5(1955), 235.2. GAUTIER, J. A., Ann. Pharm, s«, 6 (1948), 171.3. MEDITSCH, J. 0., Analyt. cbim, Acta, 31 (1964), 286.4. BRAZIER, J. N. & STEPHEN, W. 1., Analyt, chim. Acta,33 (1965),'625. '5. VENKATESWARA RAo, N. & ESWARA DUTT, V. V. S.;Z. analyt. Chem., 253 (1971), 128.6. VENKATESWARA RAo, N., KRISHNA PRASAD, K. M. M. &:RAMANA, 'P. V., Proceedings of the annual convention ofchemists, 23-27 December, Madurai, 1974.7. VENKATESWARA RAo, N. & RAMANA, P. V., cu«.Anal. Warsaw (communicated).8. ERDEY, L. & KASA, 1., Talanta, 10 (1963), 1273.9. SVEHLA, G., KOLTAI, L. & ERDEY, L., Analyt. chim,Acta, 29 (1963), 442. , .10. KOLTHOFF, 1. M., J. Am. chem, Soc., 46 (1924), 2009.11. TOLSTIKOV, V. P. & EPIK, P. A., Khim. i kliim, Tekhnol.,5 (1962), 882.12. SIERRA, F. & ASENSI MORA, G., Anales real soc. esp.fis. y quim. ser, B, 55 (1959), 377.Spectrophotometric Investigation ofOs(VI)- Thiocyanate Com~lexU. MURALIKRISHNA, K. V. BAPANAIAH, N. S. N. PRASAD &P. KANNARAOChemistry Department, Andhra University, WaltairReceived 10 March 1975; ,accepted 3 June 1975A simple and rapid method for the, spectro-photo-,metric determination of 2·5-38·0 \1~/ml of Os(VIII)ustng thiocyanate as the chromogenic reagent in,,O·5-3·0M H3PO. is described. The' reaction involvesreduction of Os(VIII) to Os(VI) which forms a 1: 1(metal-Hgand) complex with thiocyanate as is evl-deuced from the spectral data. The interference ofvarious cations has also been Investtgated,APART from the importance of thiocyanate inthyroid and brain metabolism--s->, it gainedWide popularity as a chromogenic reagent for thespectrophotometric determination of transition metalions+-". Qureshi et al.6 and Shlenskaya . et a1.7proposed spectrophotometric assay of Os(VIII) asosmium-thiocyanate complex without mentioningeither the valency state of the metal ion or thestoichiometric composition of the product formed.Thus in view of the above and in continuation of}our interest in the redox behaviour of thocyanate8-10;we have now reinvestigated the nature of thespecies in aq. medium and successfully exploredoptimum conditions, for the rapid spectrophotometricdetermination of Os(VIII) as Os(VI)-tliocyanatecomplex in aq. HaP04 medium at room temperature(25°). . , . " "A solution of Os(VIII) was prepared by dissolvingOS04 (Johnson Matthey Co., London) in O'SMNa~OH (ref. 11)' and stanardized ' iodometrically12;Os(VI) solufion was prepared bythe addition of 0·1m1 of aq: ethanol (1 :2) to'10 ml. of 10-:3M alkaline291:INDIAN J. CHEM., VOL. 14A, APRIL 1976Os(VIII) solution-s. About l'OM aq. solution of 0-64..----------------::::...--...,sodium thiocyanate (GR; E. Merck) was preparedin doubly distilled water and standardized argenta-metrically using sodium fluoresceinate as adsorp-tion indicatorw, NaCI04 solution (5M) was preparedby' mixing the equivalent amounts of HCI04 andNa2C03. All other reagents used. were of ARgrade and all dilutions were made with deionizedwater., Procedure - Phosphoric acid (1-5 ml; 8 5%, BDH)was mixed with sodium thiocyanate solution (5-16ml 0·5M) in a 25 ml volumetric flask. The solutionwa's made up to the mark after the addition of analiquot of Os(VIII) solution containing not morethan 950 [Jogof the metal ion. The homogeneoussolution was left for 10 min for full colour develop-ment. .The absorbance of the resulting orange-yellow-coloured complex was measured on a HilgerSpekker absorptiometer using filter No. 1 againstthe reagent blank.In the presence of excess [thiocyanate], superim-posable spectra (Spectron~c 20,. Bausch & Lomb)were obtained for the osmium-thiocyanate complexin H3P04 (0'5M) or HCI04 (0'5M) media, the Fig.metal ion being added in octavalent or hexavalentstate suggesting the formation of the complex withOS(VI)15. Spectra with various metal ligand molarratios (1 :1, 1 :2, 1 :3, 1 :10) in 0'5M HCI04 and atan ionic strength of 0·70 suggest the presenceof a single absorbing species, having the absorptionband in the region 440-470 nm. .The empirical formula of Os(VI)-thiocyanatecomplex was determined by the methods of Bentand Frenchw Yoe and Jones17 (Fig. 1) and Manningand Harveyi8. All these methods unequivocallysuggested the formation of a complex with a metalto ligand ratio of 1:1. -It was observed that no detectable change in theabsorbance occurs at [H3P04] = 0·5-3·OM. Thecolour development was found to be slow when equalconcentrations of other mineral acids were employed.The absorbance of the complex was found to be Referencesconstant when 300 molar excess of the ligand waspresent in the solution. Higher [ligand] had littleeffect on the colour of the complex.It was found that the system obeys Beer's lawin the concentration ion range of 2,5-38 [Jog/mlof Os(VIII). From Ringbom's plot19 the opti-mum range for the determination of Os(VIII) wasfound to be 9·0-27·0 [Jog/ml. Sandell's sensitivitywwas calculated to be 0·0048 [Jog/cm2•The ions Cd(II), Mn(II), Ni(II), Zn(II) , Mo(VI) ,Cr(III), W(VI) , As(III) , Sb(III), CI-, NO; -and CI04(10 mg each), Sn(II) (5 mg) and Pd(II) and CN (2 mgeach) did not vitiate the determination of Os(VIIl)by the present procedure while even trace amounts ofAu (III) , Ru(III) , Rh(III), Ir(IV), Pt(IV), Zr(IV),Fe(III), Co(II) and Cu(II) interfered seriou~ly. Theinterference of these cations was obviated bydistilling Os(VIII) by the procedure of Steele andYoe21,The saturated solution of OS04 was reported tobe as good an oxidant as brom.ine water~2. In viewof the -good reducing properties .of thiocyanate .areduction-cum-complexation reactIon23-25 was anti-2920·00·56• 0110ucCI&ljoCt0'320'240·16o·s 1·0 1·5 2'0 2·5[SCN-J/ [Os(VllJ1-Mole ratio plot {[Os(VI)]=1'6x10-4M;=0'50M; !J.=0·70M: cell length = 4 em}3-0 3·5cipated. A thorough study of the spectral datausing an excess of [ligand] revealed that the colouredspecies formed with Os(VIII) and Os(VI) were oneand the same. The absorbance of orange-yellowOs(VI) -thiocyanate complex was stable for about48 hr at room temperature (25°). The likelihoodof further reduction to Os(IV) and complexationis eliminated by the fact that the spectrum ofOs(IV) remains unaltered in the presence and in theabsence of thiocyanate.The authors are grateful to the CSIR, New Delhi,for the awards of senior and junior research fellow-ships to two of them (K.V.B. and N.S.N.P.) and tothe University for a research fellowship (to P.K.R.).1. STANISLAW,B., Endokr, pol., 21 (1970). 87; Chern, Abstr .•74 (1971). 721P.2. FRENCH, C. M.• Frog. Brain Res .• 29 (1968), 29; Chcm,Abstr., 72 (1970), 19667f.3. YAMADA.T. & JONES, A. E .• Endocrinology, 82 (1968),47; Chem. Abstr .• 68 (1968). 36422g.4. RIZYCKI, C., Chemia analit .• 11 (1966),447.5. ROZYCKI, C., Chemia analii., 15 (1970), 3.6. QURESHI, M. & MATHUR, K. N., Z. analyt. cse«; 242(1968). 159.7. SHLENSKAYA,V. I. & KHOSTAVA,V. P., Zh. analyt. cu«,23 (1968), 237.8. MURALIKRISHNA.U. & BAPANAIAH, K. V., Z. physik.Chem. (Leipzig), 255 (1974), 16.9. MURALIKRISHNA,U. & BAPANAIAH,K. V., Indian]. Chem.,12 (1974), 880.10. MURALIKRISHNA,U. & BAPANAIAH, K. V .• Z. physik.Chem. (Leipzig), 256 (1975), 225.11. NORKUS. P. K. & STULGENE, S. P .• Z. analyt. Chem.,20 (1968). 443.12. BEAMISH, F. E., The analytical chemistry of noble metals(Pergamon Press, Oxford), 1966, 325.13. MAJUMDAR, A. K. & SENGUPTA, J. C., Analytica chim.Acta, 21 (1959), 260.14. VOGEL, A. I., A textbook of quantitative inorganic analysis(Longrnans, London), 1969, 82. .15. MAJUMDAR.A. K. & SENGUPTA. J. C., l- Indian chem,Soc., 38 (1961), 625.16. BENT, E. E. & FRENCH, C. L., ]. Am. chem, Soc., 63(1941), 569.17. YOE, J. H. & JONES, A. L., Ind. engng Chern; Anal. Edn,16 (1944), 111-18. HARVEY (Jr), A. E. & MANNING, D. L., J. Am. chem,Soc., 72 (1950), 4488.19. RINGBOM, A., Z. analyt. cu-«, 115 (1939), 332.20. SANDELL, E. B., Colorimetric determination of traces ofmetals (Interscience, New York), 1959, 83.21. STEELE, E. L. & YOE, J. H., Analytica cbim. Acta, 20(1959), 211; Analyt. Chem .• 29 (1957). 1623.22. LATIMER. W. H., The oxidation states of the elements andtheir potentials in aqueous solutions (Prentice-Hall,New York), 1952,232.23. DESHMUKH. G. S. & TATWAWADl, S. V., Ann. Chim. Roma,50 (11i60). 428.24. WILSON, A. M. & MEFARLAND, O. K., Analyt. cu«,35 (1963). 302.25. GOTSCHALK. G., Z., analyt. Chem., 187 (1962), 164.Promethazine Hydrochloride as a NewReagent for SpectrophotometricDetermination of Pd(II)H. SANKE GOWDA & B. KESHA VANPostgraduate Department of ChemistryUniversity of Mysore, MysoreReceived 2 April 1975; accepted 20 May 1975Promethazine hydrochloride (PH) forms a red-colour-ed 1: 1 (metal: Ilgand) complex instantaneously withPd(II) at a pH 1·3-4,0. The sensitivity of the reactionis 0·027 11~/cma and the molar absorptivity is 3·86 x 103litre mote'? em'? at 470 nrn, Beer's law is valid overthe concentration range 0·4-20'0 ppm. However, theoptimum range for the effective colorimetric determi-nation is 2·0-19·0 ppm. The stability constant of thecomplex at 27° and pH 3·0±0·1 is found to be 5·1.CAVATORTAl studied the reaction of PdCl2 withpromethazine hydrochloride (PH) and usedit for the colorimetric determination of the latter.Sanke Gowda and Ramappa" studied the complexformation of Pd(II) with diethazine hydrochloride.The present paper describes PH as a sensitive re-agent for the spectrophotometric determination ofPd(II).The stock solution of Pd(II) was prepared bydissolving raci, (0·9886 g) of Johnson M~tthey gr~dein dil. HCI (Analar) and diluted to 1 htr~ to gIVe0·1 M with respect to HCI. The solution wasstandardized gravimetrically using dimethyl gly-oxime. It was further diluted to give a standardsolution containing 30 ~ Pd(II)/mI. The stocksolution of PH (May & Baker g:ade) was pr~p~redby dissolving a known amount in doubly dlst~lledwater and stored in an amber-coloured bottle m arefrigerator. . .Walpole buffers" in the PH range 0·65-5·20 wereprepared using sodium a~etate .(lM) and.HCI (1M)solutions. Solutions of diverse IOns of SUItable con-centrations were prepared using AR grade rea%ents.Procedure - To an aliquot of Pd(II) solution (10to 500 (Jog)in a 25 ml volumetric flask were added5 ml of Walpole buffer (PH 2·6) and 3 ml of PH,solution (0·2%) and the volume made up to ~hemark with doubly distilled water. The solutionNOTESwas mixed well and the absorbance measured at470 nm against a solution containing all-the reagentsexcept Pd. The amount of Pd was read froma standard calibration curve.PH forms ared-coloured complex with Pd at PH1·3-4·0. If the PH of the medium is >4, theabsorbance readings are not constant and above 7a white precipitate is formed. A maximum colouris produced when the mixture contains a thirteen-fold [reagent] with respect to (metal ion). The redcomplex exhibits Amax at 466-476 nm. The reagentunder similar conditions does not absorb at thiswavelength. The absorbance values remain con .•stant for 24 hr and at 5-97°C. Beer's law is validover the (Pd) range 0·4-20·0 ppm. However, theoptimum concentration range evaluated by Ring-born's method+s is 2·0-19·0 ppm. The Sandell'ssensitivity, as calculated from Beer's law data, is0·027 {Jog/cm2and the molar absorptivity is 3·86x103 litre mole'< vcrrr+, There is no appreciablechange in the absorbance or in colour intensity ofthe complex if the order of addition of reactants .arechanged.Job's method of continuous variations-? ([1. = O·lMNaNOs; PH 3·0±0·1; temperature 27°±1°C; Amax470 nm) and the mole ratio method indicate theformation of 1:1 complex between the metal andreagent. The observations recorded at 450 and 500nm also confirm the existence of only one complex.The apparent stability constants of the complexcalculated from the absorbance data by (a) methodof Foley and Anderson? modified by Mukherji andDey-" and (b) mole ratio methods are 5·05 ± 0·1 and5·15 ± 0·1 respectively. .The following amounts ({Jog/ml)of foreign .ions arefound to cause error <2% in the determinationof 10 (Jogof Pd(II) per ml: Os(VIII), 40; Pt (IV) ,12; Ir(III), 12; Rh(III), 9; Ru(III), 0·6; Ni(II), 575;Cu(II), 500; Co(II) , 96; Fe (III) , 4; C1-,7500; NOa,2850,F-, 1500; S024, 1000; acetate, 600; POi-,550; Br-,180 and 1-, 0·8. The present spectrophotometricmethod for the determination of Pd(II) using PHhas the following advantages over that usingdiethazine hydrochlorides: (a) Pd(II) may be deter-mined in a wider range of concentration, (b) longerstability of colour (24 hr in contrast to 4 hr withdiethazine hydrochloride), (c) insensitivity towardstemperature (5-97°C), and (d) lower amount ofreagent used.References1. CAVATORTA, L., J. Pharm, Pharmacol., 11 (1959).49.2. SANKE GOWDA, H. & RAMAPPA, P. G., Indian J. Chem.,1975, (in press).3. BRITTON, H. T. S., Hydrogen ions (Chapman & Hall,London), 1955, 353.4. RINGBOM, A., Z. Analyt; cu«; 115 (1938), 332.5. AYRES, G. H., Analyt. Chem., 21 (1949), 652. .6. JOB, P., Ann. cu«, 9 (1928), 113.7. IRVING, H. & PIERCE, T. B., J. chem. Soa., (1959),2565. - .8. YOE, J. H. & JONES, A. L., Ind. Engng Chem., 16 (1944).III.9. FOLEY, R. T. & ANDERSON, R. C., J. Am. chem. ss«, 7(}(1948), 1195; 71 (1949), 909. .10. MUKHER]I, A. K. & DEY, A: K., Analyt; chim,Acta, 18 (1958), 324; J. inorg. nuct: Chern." 6(1958). 314. '293'

Spectrophotometric Investigation of Os(VI)- Thiocyanate Complex

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Spectrophotometric Investigation of Os(VI)- Thiocyanate Complex

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