Garg, B. S.

Mehta, Y. L.

Singh, R. P.

English

NOPR

Indian Journal of Chemistry\"01. 14A, December 1976, pp. 1004-1005Spectrophotometric Determination of Os(VIII) Using2,3-Dihydroxypyridine & 5-Chloropyridine-J,3-diolY. L. MEHTA, B. S. GARG & R. P. SINGHDepartment of Chemistry, University of Delhi, Delhi 110007Received 1 October t 975; accepted 3 April t 976Osmlum(VIII) forms I: I brown complexes with 2,3-dihydroxYi>yridine (DHP) (80-foldexcess) and 5-chloropyridlne-2,3-diol (CPD) (120-folll excess), exhibiting I.max ut 230 and 310nm in the pH range 8·5-11 when the contents are heated on a boiling water-bath for 150 and 210min respectively. However, studies of both the complexes have been made in the visible regiononly (at 500 nm) using water blank. The colour systems obey Beer's law up to 7 and 8 pprn ofOs(VIII) in the case of DRP and CPD respectively. The metal-ligand composition of the com-plexes has been determined by Job's and Bent and French methods. The sensitivities of thecolour reactions between osmium and DHP and osmium and CPD are 0·0058and 0·0098 Ilg cm-'respectively. The method is very sensitive and fairly selective and compares well with manyknown methods.A LARGE number of rcagentsl-6 have beenused for the spectrophotometric determinationof Os(VIII), but the iuli-r-n t disadvantavcsare the interferences due to diverse ions and rigidcontrol of working conditions. In some of the knownmethods prior separation of osrni urn as a volat i II:tetroxide is necessary. In view of this, tlur« i~ aneed for better reagents for easy manipulat ion andbetter sensit ivit y and sclcctivi ty. The rfficacy of2.3-dihy(lroxypyri(rne (DHP) and 5-chlowpyrilli:'c-2, 3-diol (CPD) for tlte spectrophotometric det crrniua-tion of Os(VITI) wa-. therefore ill\"~stigatnl a«l lilt:results arc presented in this paper. DHP and CPDhave earlier been used for the spcctropliotomot riedetermination of iron and palladium". III t lu:present method, although platinum and some otherbase metals interfere during the normal course ofdetermination, these interferences can be casilvcircumvented by choosing the appropriate m<1ski!'f~agents. DHP has also been used for the deter-mination of O,.(VIII) in synthetic mixtures,Materials and MethodsUnicarn SP 600 and Beckman DU-2 spcctropho to-meters were used for measuring absorbance illthe visible a-id UV f<~gions respective-ly. A MctrolimE 350 PH meter. with saturated calomel a-iel gla-;,;electrode assembly, w as used for PH measun-mon t s.DHP (Fluka) and CPI) (K & K Laboratories)were used as such. Stock solutions of DHP a-idCPD w. rr: prepared in ctha iol by r.ifluxing on awater-bath.TIlt! stock solution of Os(VIII) was prepared bydissolving ampoules of OS04 (Johnsoll Matthey,London] in 2N NaOH as described by Ayres andWdls8 and standardized bv th,' method of Klobbic".All other chemicals I~secl were of AR gra(le.Buffer solutions were prepared followir-; the COIl-ven tional methods.Procedure - To an aliquot containing 1·5-5·2or 1'2-7,1 ppm of osmium was added an excess1004(SO-fold ill the case of DHP aud 120-fold in the caseof CPD) of the rca.~(:l\t solut iou. After adjustingthe PH to 10 by a'l.1iJ)~ 3 ml of ammonium chloride-ammonium hydroxide buller (PH 10), the resultings"lnlioll \Va'; lvatcd for the nquircd time period(105 mill for DIlP aud 210 ini n for CPD) 011 aboi liiu, wain-bath, cooled. transferred into a 10 11111I11',bllril'g flask, vclumo made up by adding doubly.Iist ilk-d "'atcr, and the absorbance measured at500 11111. The amount of osmium was evaluatedfrom t h« cal ibratio: curves rlrawn under similarcondit ions.Results and DiscussionThe ahsorpt ion spectra of solutions containinga fix.«! amouut of ()~(VlIl) an.l different concen-t r.u ious IJf t h-: lii;a"ds and at different PH valueswere recorded after the! solutions wrrc lu-at cd underreflux. In all t h. CtSl',;, t he complexes showed twoahso rpt ion maxima at 230 a-id 310 11m. However,till! Sllltli,',; liav« bee". carriCll out in lh,: visible region(500 11m) because t lurc is less steep fall ill theabsorbaicc at 500-520 nm aurl the iutcrferenccsdue to ma: y colourlcss iOIlS, which would otherwisein krft-rl' scrion- ly ill the lJV range, are much lesspronounced. 1']\\; ahsorpt 'OJ'. maxima of the corn-ph-Xl':' remained w'cita'lg('d even WllL:!J differentproportions of osmium and l;ga!lds were mixedsllgg('-;1i!:g till! Iormnt ion of only one complex illboth t l.c cases.It \\':L'i o!J"ITv,·tl that almost !lO complex formationtook place iJ1. tho cold, hut wlu-n solutions wen:hta tcd OIl a hoilillg water-bath Icr 105 min if: thecase of DHP a.i.l for 210 mill ii. the case of CPD,the colour starte-d d"vdoping and filIally a browncolouratio: resulted. Further l>,eati:lg did not havea-iv -ncct on the absorba-ice. Therefore, in bothth.~ cases, tit" OJ'i tell Is wo rc heated for 15 min moret11a:1 the minimum ht'atil'i~ time required for fullcolour development. The absorbance was measuredagainst water blank as the same clue to the reagentsMEHTA et al.: SPECTlWPHOTOMETRIC DETERMINATION OF Os (VIII)was practically negligible at 500 nm. The complexeswere found to be stable for at least 24 hr, after whichthe absorbance started decreasing slowly.. It was observed that the absorption of complexesincreased with the increasing pH, attained amaximum value in the PH range 8'5-11, and there-after started falling. Hence, the studies were carriedout at pH 10 using ammonium chloride-ammoniumhydroxide buffer, the constituents of which do notcause variation in the absorbance.It was also observed that the excess ligands(80-fold in the case of DHP and 120-fold in the caseof CPD) were necessary for full colour development.Beer's law and sensitivity -- The system obeyedBeer's law up to 7 ppm of Os(VIIl) in the case ofDPH and up to 8 ppm ill the case of CPl). Thesensitivities of the colour re-actions in terms ofSandell's definition arc 0·0058 and 0·0098 It:; of oscm-2 for DHP and CPD respectively. Tl«: optimumranges within which accurate determination ofOs(VIII) can be carried out, as deduced fromRingbom plot, are from 1·5 to 5·2 <1]'.(1 from 1·2 to7·1 ppm of Os using DHP and CPD respectively.Composition of the complexes - The compositionof the complexes was detcrmir cd by Job's (finalmolarity of the solutions being 1 X 10-3M) and Bentand French (final molarities of the metal a.id IigandForeign ion addedTABLE 1- EFFECT OF DIVERSE IONSFluorideOxalateTartrateBorateCitratePhosphatePersulphateNitriteNitrateCyanideBromideIodideSulphiteAcetateRu(III), rhodium(III), paJladium(lI),iridium(III), and platinum(IV)Cu(II)Zn(II)Cd(II)Hg(II)Ni(II).Mn(lI)Al (III)Mg(II)Sc(III)Ba(II)Mo(VI)Sn(IV)In (III)Pb(II)Gd(III)U(VI)Co(lI)EDTATolerance limitsusing*DHP(ppm)500500500100500805005008005050080500800320201025t2025t1St5025t502525t25tlOtsot1525t1,100CPD(ppm)5050505005050015090702580100toO50020152550sot501525t5030t503020t20t15t50t50sot200*ConcentratioI.1 at which not more than 2% deviation inthe absorbance IS obtained.tGot precipitated and removed by centrifugation.TABLE 2 - DETERMINATION OF Os (VIII) INSYNTHETIC MIXTURESOs(VIII)added(ppm)555Ir added(ppm)Ru added(ppm)Pd added(ppm)Os(VIII)found(ppm)4·904·954·901111150·12·25·50·551·40·55solutions being 5 X 10-·5M and 1 X 10-3M respectively)methods. Both the methods showed the formationof 1:1 (metal-ligand) complexes.Both the complexes were shown to be ionic illnature, as they were not extracted ir.to the commonorganic solvents. Furfher, they were retainedalmost completely by the anion exchange resin(Amberlitc IR-400, chloride form) and their solutionspa~sed llllChalJf?cd through the cation exchangeresm, establishing thereby their at.ionic nature.However, in the absence of further proofs, notentative structure can be ass:gu~d.Effect of added ions - The study was carried outill solutions con ta ining 5 ppm of osmium ardthe desired amounts of toreign ions. After followingthe recommended procedure the absorbances werenoted. The results are recorded in Table 1. Someof th~ ions sucl~ as tl~ios~llphate, thiocyanate andsulphide and thiourea inhibit the colour formationeven when present ill traces, Iron interferes seri-ously in the determination.In the case of DHP, EDT A and fluoride wereused as masking agents to remove the interferencesof the ions. Following are the results, the maskableamounts (in ppm) being given ill the parentheses:Rll(III) (20), Rh(III) (20), Pcl(II) (20), Ir(III) (20),Pt(IV) (20), Cu(lI) (50), Ni(II) (50) and Pb(II) (50)with EDTA, and Fe(III) (50), ~1(III) (50), Sn(IV)(50) and MIl (II) (50) using fluoride.Determination of Os(VIII) in synthetic mixtures- On account of the difficulty in getting thenaturally occur ring ores of osmium, different syntheticmixtures were prepared and an alyscd as follows:To the synthetic mixtures were added excess ofEDTA (1100 ppm) followed by DHP solution a-idthe amount of Os (VIII) was determined as describedabove. The results are recorded in Table 2.AcknowledgementThe authors are grateful to the CSIR, NewDelhi, for the award of a senior research fellowshipto one of them (Y.L.M.).References1. BEAMISH, F. E., The analytical chemistry of the noblemetals (Pergamon Press, London), 1966.2. AGARWALA,B. V. & GHOSE, A. K., Tulanta, 20 (1973), 129.3. McDONALD, C. ,V. & CARTEL, R., Analyt. cs-«, 41(1969), 1478.4. SANDELL, E. B., Analyt, Chem., 16 (1944), 342.5. STEIGER. B., M'ikrochemie, 16 (1934), 193.6. BOLTZ, D. F. & MELLON, M. G., A nalvt: Chem., 46 (1974)233R. '7. KUSHWAHA, V., KATYAL, M. & SINGH, R. P., T'alanta,21 (1974), 763.S. AYRES, G. H. & WELLS, ,V. N., A nalvt, Chem., 22 (1950)317. J'9. KLOBBIE, E. A., Chem. Zentbl., 11 (1898), 65.1005

Spectrophotometric Determination of Os(VIII) Using 2,3-Dihydroxypyridine & 5-Chloropyridine-2,3-diol

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Spectrophotometric Determination of Os(VIII) Using 2,3-Dihydroxypyridine & 5-Chloropyridine-2,3-diol

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