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The colorimetric determination of iridium by O-dianisidine
VOL.
SPEGTROPHOTOMETRX’
15 (1956)
OF
RARE
EARTH
MiSTURES
363
The molar absorptivitics for most of the rare cnrths have been ticterminccl at the wavelengths of the various analytically significant absorption bands. These molar absorpttvitics have been determined on the I3cckmz.w lQodel UU spcctrophotomctcr with and without a photomultiplicr attachment as well as on a C&try ivIodc1 1.l recording spectrophotomcter. The techniques and analysis of rare earth mtxturcs arc discussed. instrumentation neccssnry for the satuifactory A general procedure is presented wlrich has teen found most uscfu1 for the routrnc annlysrs of a wide variety of rare earth mi.xtures. 1,‘;ibsorptivitd rnol&xrlaire rle la plirpart tics tcrres rarcs a fit& dBtcrniin62 aux longucurs cl’onde clcs bandcs d’absorption signtficatlvcs rlu point de VW nmtiytiquc. Ccls &tcrminntions ont &t& effcctudcs 21 I’aidc tl’un spcctrophotombtre Bcckmen mod&It: r)U. RVCC 011 sans npparcil auxiIi&c DVCC rn~litil~ll~~tcur a &mission second&m tit mSme qu’au moycn tl’un sp~ctropltotoili~~r~ et f’opparcillagc n&xss;tircs pour ottcnir tics enrcgistrcur vary mod& 84, I ss tcchniquew analyses aatisfaisantcs tic m&langcs clc tortes rarcs sont ciiscut&i. tine mdthacle gdndrnlc OL(. tlderltc; cllc s’cst montrPc trbs utile lxtur tics au:Llyscs cn shit tl’unc grundc varidtC dc mclhngcs tic twrcr I _ rarcs.
%WS*\~~~I~.NFASS~~NC; I>ic molekulnrc p\bsorptlon tier meistcn seltcncn Ertlen xvurdc LCI tlcn Wcllcnliingcn rlcr vcr13icsc 1Jcstimni11ngcn wurclcn schicdtncn analytisch wichtigcn hbsorptionst,snclcll bcstimmt. nyit cincm f3cckman-Spektropfwtomcter ~~oclcl1 l>U mit ndcr ohnc Sukrtnti!irclcktroncnv~r~-iclfactter..%us:rtzgcr9t uncl mlt cmcm Cam-Rc~isttiorspcktropilotomctcr >lociell 14 ausgefuhrt. Die z~ar AusfiillrtlnK lxfrwrligcntlcr Anaiyscn wn Gcmischcn scltcner Krden crfr~lrlcrl~cltcn VcrfiLhrcn uncl Kinc allgcnicine I\Icthodc. clic sich xur r\usfiihrnn)= von RoutineAppnrrLtc wcrclrn crbrtcrt. an;~Iyscn schr ver~chitdencr C&2mischu van scltcncn 15rclcn bosondcrs nhtzlich erwicscn hat, wirtl bcschrielxn.
THE
COLORIMETRIC DETERMINATION IRIDIUM BY O-DIANISIDINE
OF
There have been comparatively few procedures recommended for the colorimetric determination of iridium. Of four that have heen developed usefully, three*~G~d are relatively insensitive compared to the fourth*; all four involve heating iridium solutions with various colour-forming reagents, and our experience has 12t*fcreucc?s
p.
366
3%
S.
S.
13EliMAN
id
al.
VOL.
15 (rqg6)
shown that the temperature and duration of heating may considerably influence the precision attainable. in this communication we describe a simple procedure that we have found useful for clctcrmining small amounts of iridium after isolation from other platinum metals. When o-dianisidinc in acetone is acltlcd to an acidic solution of chloroiridatc(rV) a bright red soIution is formed, the colour of which sIowly fades. l-fowcver, if the solution is only slightly acidic (pfr>3) ;L green solution is formed when the reagent is i~dclcd which quickly clu~rrges to orange. If this orange solution is acidified with conccntratcd hydrochloric acid an intensely colourcd purple solution is formed which is quite stable. This purple solution possesses a spectrum with ;m ahsorbancc maximum at 530 mp when me;wurcd against a reagent blank (Fig. I). __-_.^__. -___--_*- --. ---__-_ -1
WC hvc no cxperimcntal basis for speculation concerning the reactions to which thcsc colour changes correspond, but it stems IikcIy that an oxidation of the organic base is one step. Conscqucntly, intcrfcrcncc by oxidizing aGents, as well as by the other platinum mctols, rather restricts the application of the mcthocl. It is a fact, howcvcr, that few specific colorimctric reagents for platinum metals have been of various physical methods of separation, discoverccl. The recent devclopmcnt for instance by partition chromatogralA~y4 or by ion cxch;lngcW, has made it casicr to isolate smnll amounts of iriclium than before, but there is still need for 8 simple scnsitivc means for its dctcrminntion.
A stock
solution of pure ittnmoniuw cl~lort~tritIiLtc( I V) in o.og~If l~yctr0chl0ric acid was pqxwcct, ntanctnrcliactl by poLcntiornctrIc trtrntton with iron( 1 I) sulpltntc~. ‘I’hn stock solution, wf&zh cont:rinccl 1.HCJnig of irltlium per ml WilS tlllutotl fifty-fold for tlic cspcrirncnts tlcscribcd below. h o.s(!;, solution (w/v) of o-tlianisitlinc (Urltish Ih-ug ~iou~os) WRS prcprrccl m acetone. This solution was quite stable and ~lxwect no clinrryc cm prolonged standing. A 0.1 AI acetic acid-sodium acetate bttffcr of pH 4.7 was prcparccl hy tnizting cqunl vcdutncs of 0 .rM xctic acid and 0.2&I sotlitlm ncctntc. :\I1 CtlL~nlic_XLlS Itsccl wow nf iLrliLl~tiCiL1 rmgcnt or C.P. gmtle. iLnC1
i~cferonccs
p.
3ciG
In experiments to find optimum conditions for the colour reaction the foiiowlng basic proccdurc was followed. A solution containing: 189 kg of iridium was transfcrrcd to a zs-ml voiumctric flask. and o-ciianistdine soiutioi! and buffer solutlon were added. The sampic was then made up to volume with 102 hycirochlortc acid, and the absodbance measured. The reaction did not proceed if the per of the !ricilum solution was icss than 3 Adciitmn of I ml of o-tlianisidinc solution. which is basic, rniscti the PH of an triclium solution that was orlginnilv 3 to 4.3. The absorbance of the solution incrcnsed slightly with increasing pH, but at the same time the prectsion fell off, pcrhapu owmg to partial hytirolysls of the chioroiritlatc solution. With an acetic actd-sodium acctatc buffer of pu 4.7 iridium coulcl be determined with maximum senSitivity consistent with good precision.
lridlum,
1*‘1g. 2. r\i~sorl~nncc us. conccnlr.~tion h. Stock 13.
Act11
for iridium(lV) irltlllllll WJh~tiCJllS. iridium Solutions.
pqp.m.
solutions
with
o-til;Lnisltl~nc.
‘r’hc absorbance, measured against a reagent blank, varied with the quantity of rcagcnt nritictl but was a maximum for 0.75 to I .o nil of the o.s’T<‘, o-siianisltiinc reagent holutlon. One ml was chohcn for all suhscqucnt cietrrminntionb. .\ blank prqxlrcti wtth the o-diitnisidinc rengcnt sho~cri a con%tilnt :~i~~orimitcc iit 5.50 III/L when ntcasurcd against SL water blank On the groan& of convcntcnce we tlccrtlcrt to make all mcasurc1:~2nts of aitworbancc of iridium solutions against a water blank. T3ccr’s law is foliowcd from z to 10 c/g per ml. A ccmccntration of 17 146 per ml rcprcscnts approximntciy unit ahsorbancc. Ijcinw it concentration of 2 pg per ml there IS littlc change of absorbance with chnngc of concentration of iridium. This i% shown in Ftg. t. ‘l’hcsc curves wcrc plottcd from data obtaincti with a water blank: the iL~J%XilnnCc due to the cl-tiianisitiinc l~hiiic is given by the tntcrcept on the vertical axIS, Curmrislv enough, if the Straight-linf! portton of the cttrvc Is cxtrapolatcd to zero conccntrat*on of iri&m tt passes through the origin Five rcplicatc samples, each containing 1Scjpg of irictiiam In a finat volume of 2? ml, gave a mean absorbance of 0.478 with an average ticviatron of 0.0004 or 0.08 y{,. No change in the absorbance of these solutions was found after qG hours. Pallacl~um. platinum, rhodium, nickel. chrt>mium, rrntl copper wcrc found to tntcrfcrc with the coiour dcvciopmcnt when present with iridium in acidic solutions. Tiic ab4nrbancc in each case, csccpt for platinum, was smaller than for the Same amount of irtciium alone. Rhodium produced the lcast lntcrfcrcnco ; wrth as fig of rhodium the absorhancc due to a89 ccg of irithum was iowcred l)p one per cent. Oxidtzing agents such as iron(lIl), golci(III), and nitric acid must be absent. Since iridium is usuaiiv present 111acidic solutions proviSion must LJC made to rcmovc the acid while retaining the iridi;rm in the quadrivaicnt state. I’his was not possible for suiphuric acid solutions, but was achicvccl for hydrochloric acid solutions by evaporating with a small amount of nitric acid and sociium chloriclc and then twice with hycirochloric acici. ‘J’hc sodium chloride kept Referewes
p.
366
366
s. S. UOKMAN
VOL.
t?t al.
15
(1956)
the iridium from baking onto the glass bcakcr during evaporation. When the residue from this trcatmcnt was taken up in water and treated by the procedure already described the absorbance was found to be smaller than that obtained for equivalent amounts of the stock solution. Thus five rcplicatc samples, each containmg r89,ug of iridium, gave a mean absorbance of 0.386 with an average deviation of o.oooG or o. I 6%,. The absorbance of these samples conformed to Beer’s law for conccntrattons above z pg per ml (Fig. z), and was independent of the amount of acid present in the original iridium solution. WC were unable to assign a cause for the dccrcasc in molar absorptivity of the solutions that had been subjected to this evaporation. We judged from the high precision obtainable that this dccreasc could not be due to reduction of a portion of the iridium from the quadrivalcnt state. We did ascertain that tho amount of sodium chloride introduced in the recommcndcd proccdurc caused no rIMXLSUI%lJ~C dccrcasc in colour of the solution. i2rcomme&cd firocrdurc In view of our findings dcscribcd in the prcccding paragraph WC dccidcd to evaporate all samples to dryness bcforc dcvcloping the colour. The following is our complete procedure. Add to each sample a few drops of conccntratcd nitric acid and I ml of a o.zoA, solution of sodturn chlorldc. Evaporate to dryness on a boiling-water bath. Take up the rcsiducs three times In a few drops of dilute hytlrochloric acid, evaporating to dryness each time before adding the next portion of acid. This evaporation climinatcs the last tracts of nitric acid which, if prcscnt, would oxidizc the rcagcnt. D~ssolvc the cvaporatcd residues in a small volume of water and transfer to zs-ml volumetric flasks, cliluting to volume with water. After mixing thcsc solutions, transfer 5 ml aliquots to z5-ml volumetric flasks. Adtl 1 ml of o-dianisitlinc reagent, 2 ml of acetic acid-sodium acctatc buffer, and dilute to volume with xzM hydrochloric acid. Mcaauro the absorbance at 530 mp (br with a filter having approximately this wave-length for maximum transmission) against a distilled water blank. It is permissible to develop the colour in the samples resulting from evaporation (that is, not taking aliquots) provided that thcsc arc transferred to volumetric flasks in a total volume of 5 ml of water. ACKNOWLICDGILMI!NT WC ilrc grateful for a grant 111aitl of this rcscarch from and previously the Rcscarch Council of Ontario.
the
Ontario
Rcscnrch
I;oundation
SUMMARY Under prcscribcd conditions chloroiridatc(lV) and o-dianisidinc undergo a scqucncc of rcactionn resulting in an intcnsc purple colour. This may bc made the basis of a photometric dctcrmination of iridium in solutions from which the other platinum metals and certain base metals have been rcmovcd.
Dans tics conditions d~lcrmindcs Ic chloroiridatc(lV) ct I’o-dianisidinc clonncnt unc sdric dc rdactions qui conduiscnt finalcmcnt h unc coloration pourprc intcnsc. Ccci pcut constitucr la base tl’un dosage photombtriquc dc I’iridium aprbs &liminatlon dc ccrtains metaux ct cn particulicr dc ccuxdu groupc clu platinc. ZUSAMMENFASSUNG Untcr bcstimmtcn Ucdingungcn gcbcn Chloroiridat(IV) und o-Dianisidin cinc Reihc von Reaktion die schll@sslich zu cincr intens purpurrotcn Farbc fbhrcn. Dies kann als Grundlagc cincr photomctrischcn 13cstimmungsmcthoclc filr Iridium dicncn, wobci cinigc Mctallc und rwar iusbcsondcrc clic clcr I’latingruppc cntfcrnt wcrden milssen.
1 G. I-f. AYRES AND Q. QUICK, Atrnl. Chem., 22 (1950) x403. a E. W. BERG AND W. L. SENN, ibid.. 27 (1955) 1255. 4" M. L. CLUETT, S. S. BERMAN AND W. A. E. MCBRYDE, .4~~~lysI,80 (rg55) 503. N. F. KrmxmR AND R. A. WELLS, ibid., 80 (1955) 735. IJ W. M. MACNEV:N ANI) 0. H. KRIIXF,, ,481al.Chern.. 28 (1956) 16. n A. 1). MAYNIX AND W. A. E. MCBRYDX. Ataalyst, 79 (1954) 230. ’ W. A. E. MCURYDE AND M. I,. CLUISTP, Con. J. Research, 28B (1950) 788. R A. D. WESTLAND AND F. E. BISAMISH, Artal. C/tern..27 (1955) 1776. Rcccived April 3rd, 195
SPEGTROPHOTOMETRX’
15 (1956)
OF
RARE
EARTH
MiSTURES
363
The molar absorptivitics for most of the rare cnrths have been ticterminccl at the wavelengths of the various analytically significant absorption bands. These molar absorpttvitics have been determined on the I3cckmz.w lQodel UU spcctrophotomctcr with and without a photomultiplicr attachment as well as on a C&try ivIodc1 1.l recording spectrophotomcter. The techniques and analysis of rare earth mtxturcs arc discussed. instrumentation neccssnry for the satuifactory A general procedure is presented wlrich has teen found most uscfu1 for the routrnc annlysrs of a wide variety of rare earth mi.xtures. 1,‘;ibsorptivitd rnol&xrlaire rle la plirpart tics tcrres rarcs a fit& dBtcrniin62 aux longucurs cl’onde clcs bandcs d’absorption signtficatlvcs rlu point de VW nmtiytiquc. Ccls &tcrminntions ont &t& effcctudcs 21 I’aidc tl’un spcctrophotombtre Bcckmen mod&It: r)U. RVCC 011 sans npparcil auxiIi&c DVCC rn~litil~ll~~tcur a &mission second&m tit mSme qu’au moycn tl’un sp~ctropltotoili~~r~ et f’opparcillagc n&xss;tircs pour ottcnir tics enrcgistrcur vary mod& 84, I ss tcchniquew analyses aatisfaisantcs tic m&langcs clc tortes rarcs sont ciiscut&i. tine mdthacle gdndrnlc OL(. tlderltc; cllc s’cst montrPc trbs utile lxtur tics au:Llyscs cn shit tl’unc grundc varidtC dc mclhngcs tic twrcr I _ rarcs.
%WS*\~~~I~.NFASS~~NC; I>ic molekulnrc p\bsorptlon tier meistcn seltcncn Ertlen xvurdc LCI tlcn Wcllcnliingcn rlcr vcr13icsc 1Jcstimni11ngcn wurclcn schicdtncn analytisch wichtigcn hbsorptionst,snclcll bcstimmt. nyit cincm f3cckman-Spektropfwtomcter ~~oclcl1 l>U mit ndcr ohnc Sukrtnti!irclcktroncnv~r~-iclfactter..%us:rtzgcr9t uncl mlt cmcm Cam-Rc~isttiorspcktropilotomctcr >lociell 14 ausgefuhrt. Die z~ar AusfiillrtlnK lxfrwrligcntlcr Anaiyscn wn Gcmischcn scltcner Krden crfr~lrlcrl~cltcn VcrfiLhrcn uncl Kinc allgcnicine I\Icthodc. clic sich xur r\usfiihrnn)= von RoutineAppnrrLtc wcrclrn crbrtcrt. an;~Iyscn schr ver~chitdencr C&2mischu van scltcncn 15rclcn bosondcrs nhtzlich erwicscn hat, wirtl bcschrielxn.
THE
COLORIMETRIC DETERMINATION IRIDIUM BY O-DIANISIDINE
OF
There have been comparatively few procedures recommended for the colorimetric determination of iridium. Of four that have heen developed usefully, three*~G~d are relatively insensitive compared to the fourth*; all four involve heating iridium solutions with various colour-forming reagents, and our experience has 12t*fcreucc?s
p.
366
3%
S.
S.
13EliMAN
id
al.
VOL.
15 (rqg6)
shown that the temperature and duration of heating may considerably influence the precision attainable. in this communication we describe a simple procedure that we have found useful for clctcrmining small amounts of iridium after isolation from other platinum metals. When o-dianisidinc in acetone is acltlcd to an acidic solution of chloroiridatc(rV) a bright red soIution is formed, the colour of which sIowly fades. l-fowcver, if the solution is only slightly acidic (pfr>3) ;L green solution is formed when the reagent is i~dclcd which quickly clu~rrges to orange. If this orange solution is acidified with conccntratcd hydrochloric acid an intensely colourcd purple solution is formed which is quite stable. This purple solution possesses a spectrum with ;m ahsorbancc maximum at 530 mp when me;wurcd against a reagent blank (Fig. I). __-_.^__. -___--_*- --. ---__-_ -1
WC hvc no cxperimcntal basis for speculation concerning the reactions to which thcsc colour changes correspond, but it stems IikcIy that an oxidation of the organic base is one step. Conscqucntly, intcrfcrcncc by oxidizing aGents, as well as by the other platinum mctols, rather restricts the application of the mcthocl. It is a fact, howcvcr, that few specific colorimctric reagents for platinum metals have been of various physical methods of separation, discoverccl. The recent devclopmcnt for instance by partition chromatogralA~y4 or by ion cxch;lngcW, has made it casicr to isolate smnll amounts of iriclium than before, but there is still need for 8 simple scnsitivc means for its dctcrminntion.
A stock
solution of pure ittnmoniuw cl~lort~tritIiLtc( I V) in o.og~If l~yctr0chl0ric acid was pqxwcct, ntanctnrcliactl by poLcntiornctrIc trtrntton with iron( 1 I) sulpltntc~. ‘I’hn stock solution, wf&zh cont:rinccl 1.HCJnig of irltlium per ml WilS tlllutotl fifty-fold for tlic cspcrirncnts tlcscribcd below. h o.s(!;, solution (w/v) of o-tlianisitlinc (Urltish Ih-ug ~iou~os) WRS prcprrccl m acetone. This solution was quite stable and ~lxwect no clinrryc cm prolonged standing. A 0.1 AI acetic acid-sodium acetate bttffcr of pH 4.7 was prcparccl hy tnizting cqunl vcdutncs of 0 .rM xctic acid and 0.2&I sotlitlm ncctntc. :\I1 CtlL~nlic_XLlS Itsccl wow nf iLrliLl~tiCiL1 rmgcnt or C.P. gmtle. iLnC1
i~cferonccs
p.
3ciG
In experiments to find optimum conditions for the colour reaction the foiiowlng basic proccdurc was followed. A solution containing: 189 kg of iridium was transfcrrcd to a zs-ml voiumctric flask. and o-ciianistdine soiutioi! and buffer solutlon were added. The sampic was then made up to volume with 102 hycirochlortc acid, and the absodbance measured. The reaction did not proceed if the per of the !ricilum solution was icss than 3 Adciitmn of I ml of o-tlianisidinc solution. which is basic, rniscti the PH of an triclium solution that was orlginnilv 3 to 4.3. The absorbance of the solution incrcnsed slightly with increasing pH, but at the same time the prectsion fell off, pcrhapu owmg to partial hytirolysls of the chioroiritlatc solution. With an acetic actd-sodium acctatc buffer of pu 4.7 iridium coulcl be determined with maximum senSitivity consistent with good precision.
lridlum,
1*‘1g. 2. r\i~sorl~nncc us. conccnlr.~tion h. Stock 13.
Act11
for iridium(lV) irltlllllll WJh~tiCJllS. iridium Solutions.
pqp.m.
solutions
with
o-til;Lnisltl~nc.
‘r’hc absorbance, measured against a reagent blank, varied with the quantity of rcagcnt nritictl but was a maximum for 0.75 to I .o nil of the o.s’T<‘, o-siianisltiinc reagent holutlon. One ml was chohcn for all suhscqucnt cietrrminntionb. .\ blank prqxlrcti wtth the o-diitnisidinc rengcnt sho~cri a con%tilnt :~i~~orimitcc iit 5.50 III/L when ntcasurcd against SL water blank On the groan& of convcntcnce we tlccrtlcrt to make all mcasurc1:~2nts of aitworbancc of iridium solutions against a water blank. T3ccr’s law is foliowcd from z to 10 c/g per ml. A ccmccntration of 17 146 per ml rcprcscnts approximntciy unit ahsorbancc. Ijcinw it concentration of 2 pg per ml there IS littlc change of absorbance with chnngc of concentration of iridium. This i% shown in Ftg. t. ‘l’hcsc curves wcrc plottcd from data obtaincti with a water blank: the iL~J%XilnnCc due to the cl-tiianisitiinc l~hiiic is given by the tntcrcept on the vertical axIS, Curmrislv enough, if the Straight-linf! portton of the cttrvc Is cxtrapolatcd to zero conccntrat*on of iri&m tt passes through the origin Five rcplicatc samples, each containing 1Scjpg of irictiiam In a finat volume of 2? ml, gave a mean absorbance of 0.478 with an average ticviatron of 0.0004 or 0.08 y{,. No change in the absorbance of these solutions was found after qG hours. Pallacl~um. platinum, rhodium, nickel. chrt>mium, rrntl copper wcrc found to tntcrfcrc with the coiour dcvciopmcnt when present with iridium in acidic solutions. Tiic ab4nrbancc in each case, csccpt for platinum, was smaller than for the Same amount of irtciium alone. Rhodium produced the lcast lntcrfcrcnco ; wrth as fig of rhodium the absorhancc due to a89 ccg of irithum was iowcred l)p one per cent. Oxidtzing agents such as iron(lIl), golci(III), and nitric acid must be absent. Since iridium is usuaiiv present 111acidic solutions proviSion must LJC made to rcmovc the acid while retaining the iridi;rm in the quadrivaicnt state. I’his was not possible for suiphuric acid solutions, but was achicvccl for hydrochloric acid solutions by evaporating with a small amount of nitric acid and sociium chloriclc and then twice with hycirochloric acici. ‘J’hc sodium chloride kept Referewes
p.
366
366
s. S. UOKMAN
VOL.
t?t al.
15
(1956)
the iridium from baking onto the glass bcakcr during evaporation. When the residue from this trcatmcnt was taken up in water and treated by the procedure already described the absorbance was found to be smaller than that obtained for equivalent amounts of the stock solution. Thus five rcplicatc samples, each containmg r89,ug of iridium, gave a mean absorbance of 0.386 with an average deviation of o.oooG or o. I 6%,. The absorbance of these samples conformed to Beer’s law for conccntrattons above z pg per ml (Fig. z), and was independent of the amount of acid present in the original iridium solution. WC were unable to assign a cause for the dccrcasc in molar absorptivity of the solutions that had been subjected to this evaporation. We judged from the high precision obtainable that this dccreasc could not be due to reduction of a portion of the iridium from the quadrivalcnt state. We did ascertain that tho amount of sodium chloride introduced in the recommcndcd proccdurc caused no rIMXLSUI%lJ~C dccrcasc in colour of the solution. i2rcomme&cd firocrdurc In view of our findings dcscribcd in the prcccding paragraph WC dccidcd to evaporate all samples to dryness bcforc dcvcloping the colour. The following is our complete procedure. Add to each sample a few drops of conccntratcd nitric acid and I ml of a o.zoA, solution of sodturn chlorldc. Evaporate to dryness on a boiling-water bath. Take up the rcsiducs three times In a few drops of dilute hytlrochloric acid, evaporating to dryness each time before adding the next portion of acid. This evaporation climinatcs the last tracts of nitric acid which, if prcscnt, would oxidizc the rcagcnt. D~ssolvc the cvaporatcd residues in a small volume of water and transfer to zs-ml volumetric flasks, cliluting to volume with water. After mixing thcsc solutions, transfer 5 ml aliquots to z5-ml volumetric flasks. Adtl 1 ml of o-dianisitlinc reagent, 2 ml of acetic acid-sodium acctatc buffer, and dilute to volume with xzM hydrochloric acid. Mcaauro the absorbance at 530 mp (br with a filter having approximately this wave-length for maximum transmission) against a distilled water blank. It is permissible to develop the colour in the samples resulting from evaporation (that is, not taking aliquots) provided that thcsc arc transferred to volumetric flasks in a total volume of 5 ml of water. ACKNOWLICDGILMI!NT WC ilrc grateful for a grant 111aitl of this rcscarch from and previously the Rcscarch Council of Ontario.
the
Ontario
Rcscnrch
I;oundation
SUMMARY Under prcscribcd conditions chloroiridatc(lV) and o-dianisidinc undergo a scqucncc of rcactionn resulting in an intcnsc purple colour. This may bc made the basis of a photometric dctcrmination of iridium in solutions from which the other platinum metals and certain base metals have been rcmovcd.
Dans tics conditions d~lcrmindcs Ic chloroiridatc(lV) ct I’o-dianisidinc clonncnt unc sdric dc rdactions qui conduiscnt finalcmcnt h unc coloration pourprc intcnsc. Ccci pcut constitucr la base tl’un dosage photombtriquc dc I’iridium aprbs &liminatlon dc ccrtains metaux ct cn particulicr dc ccuxdu groupc clu platinc. ZUSAMMENFASSUNG Untcr bcstimmtcn Ucdingungcn gcbcn Chloroiridat(IV) und o-Dianisidin cinc Reihc von Reaktion die schll@sslich zu cincr intens purpurrotcn Farbc fbhrcn. Dies kann als Grundlagc cincr photomctrischcn 13cstimmungsmcthoclc filr Iridium dicncn, wobci cinigc Mctallc und rwar iusbcsondcrc clic clcr I’latingruppc cntfcrnt wcrden milssen.
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