Handa, A. C.

Johri, K.N.

English

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INDIAN J. CHEM., VOL. 14A, APRIL 1976Selective Microdetermination of UraniumUsing Weisz Ring Oven Technique: Applicationto an Indirect Determination of TraceAmounts of Arsenic in TobaccoA. C. HANDA.Department of Chemistry, Hindu College, Maurice NagarDelhi 110007andK. N. JOHRIDepartment of Chemistry, University of DelhiDelhr 110007Received 31 August 1974; accepted 20 May 1975A procedure for the rnlcrodeterrnlnatton of uranylion!' in the presence of a large number of adverse ionshas been described involving the use of the Weisz ringoven. The chromogenic reagent that has been ern-ployed is the schiff base of N,N-diIllethyl-p-phenylene-diaIlline and salicylaldehyde which, under the specifiedconditions, gives a red-coloured product with uranylions. The visual identification range has been foundto be 0'07-1'5 I1gof uranyl ions present in the 22 rnrndiameter ring. The present procedure for uranyl ionshas also been extended to the trace amount deterrntna-don of arsenic in tobacco.IT has been observed that N,N-dimethyl-p-pheny-lenediamine salts give red coloured protonated-schiff bases with aromatic aldehydes like salicyll-adehyde: This red compound when treated withammonia turns yellow due to the formation of non-protonated form.OHc):H=N~ (CH,1+2NH4CI[YELL~W ]. The'yellow compound when treated with uranylions produce a red-colouredproduct2, the intensityof which-depends directly on the amount of uranylions.. , This reaction has been utilized in the presentstudies for 'a highly selective microdeterminationof-uranyl ions employing ring.oven techniques= alongwith an indirect determination of trace amountsof ·arsenic in tobacco. ..A .We~s~,rin~ oven (~?-tional Appliange 'Co., Por~-lp.n~h,·,Oregonf-USA) wltl;l:a suitablecpower unityielding 25 V from 220 VI50 cycles ac-rnains, wasused. A microsyringe (Hamilton Co. Inc.,Whittier, California, USA) of minimum 1 {Jolcapacity for the application of test solutions wasemployed. Filter paper circles (Whatman No. 41,55 mm diam. were washed free from iron with O'IMHCl on the ring oven and then thoroughly washedwith doubly distilled water, dried and used.Uranyl nitrate and sodium arsenate solutions wereprepared in water containing a few drops of dil.AcOH. Doubly distilled and deionized water andAR grade reagents were used throughout., Preparation of the reagent - In a test tube, 10 mlaq. 1% solution of N,N-dimethyl-p-phenylenedi-amine dihydrochloride (E.Merck) was mixed with1 ml ethanolic 10% solution of salicylaldehyde andimmersed the test tube for a few min in a boilingwater-bath. The contents of the tube were cooledand added iust sufficient amount of ammoniasolution (1:5)"when the blood-red solution changedto yellowish brown (addition of ammonia must bedone just before the experiment).Determination of U(VI) ions - A circle of What-man No. 41 filter paper was placed on the ring ovenset at 100-110°Cand a known amount of uranyl ionstransferred to the centre of the filter paper bymeans of a micro-syringe and the paper dried. Next,a drop of aq. sodium arsenate solution (5%) wasapplied followed by one drop of aq. ammonium"acetate (10%) and a drop of dil. AcOH: The paperwas dried when all the uranyl ions were fixed asuranyl ammonium arsenate .. The paper was re-'moved from the oven and washed thoroughly ona suction pad first with luke warm water and thenwith cold water. The paper was carefully removedfrom the suction pad and placed again on the ringoven. The fixed uranyl ions were washed into thering zone with O·OlM HCl, the paper dried andsprayed with the reagent, and dried at roomtemperature. A sharp red ring against a yellowbackground indicated the presence of uranyl ions.After 10 min the intensity of the red ring wascompared visually with the red rings comprisingthe standard scale prepared by taking 1, 3, 5, 7, 9,11, 13 and 15 (Jo1 of the standard U(VI) solution(0·1 mgjml) and the amount in the unknown ringcomputed.The visual identification range of the proposedmethod w~ foun~ to be 0·07 to 1·5 {Jog of uranyl ionswhen the rmg diameter was 22 mm. Outside thisrange visual comparison was difficult. Results ofsome typical experiments are given in Table 1.Determination of arsenic in tobacco- NaOH (3 g)was fused in a 100 ml nickel crucible, cooled andTABLE1 - DETERMINATIONOF U02(II)U02(II) (!D-g/ml) . ErrorTaken(%)Found0·45 0·46 +2'20'10 0·10 0'00'35 0·33 -5'70'65 0'62 -4'0 ..0·90 . 0·93 +3'3TABLE 2 - DETERMINATION OF ARSENIC IN TOBACCOSample Amount Amount AmountNo'. of of oftobacco arsenic arsenictaken taken found(g) (fLg) (ug)10 10'315 15·420 20·750 49·1A 5 4,5B 7 6,3C 9 3,5D 6 5'8E 10 4·7Error(%)+3'0+2,7+3'5-1'8tobacco sample (1 g) and Na202 (1·5 g) were addedon to the solidified mass. It was heated gently for10' min while adding Na202 (2 X 1 g) intermittentlyuntil there was a complete decomposition of theorganic matter.The above procedure was repeated with more oftobacco and Na202 till 5 g of tobacco sample hadbeen decomposed. The crucible was finally heatedfor 15 min, cooled and water (15 ml) added. Thecontents of the crucible were warmed on a steam-bath until the melt was completely disintegrated.The solution was centrifuged and the residue washedwith water. The centrifugate and washings werecollected in a 100 ml conical flask, acidified with HCI(6M) and boiled gently to decompose peroxide. Thesolution was cooled and cone. HCI (15 ml) addedfollowed by aq. KI (2 ml, 15%) and SnCl2 solution(1 ml, 40%) in conc. HCI. The contents were kept for30 min at room temperature. Zinc metal (3-4 g)was added and the evolved arsine (AsHs) decomposedto metallic arsenic by heating the tube. Metallicarsenic' was dissolved in a minimum amount of hotHNOs and the resultant solution neutralized withdil. NaOR. It was reacidified with AcOR (2N) andthe final volume made up to 2 ml by evaporation anddilution. An aliquot of the solution was subjectedto the ring oven method as described above wherebythe arsenic content of tobacco was determined andthe results are given in Table 2. The efficacy of theabove alkaline peroxide fusion method was checke.dseparately by ring-colorimetric and volumetnc(potassium bromatej'' methods. In both the methodsknown amounts of arsenic as arsenic trioxidewere taken. A few representative ring colorimetricresults have also been incroporated in Table 2.Uranium forms a red insoluble chelate with thereagent under the specified conditions. The inter-ference of various foreign ions was studied bydeveloping rings for U02(Il) ions with and withoutthe foreign ions taken in varying amounts up to 25fLg. The ions which did not interfere in the pro-cedure are: NH!, u-. Na-f, K+, Rb+, Cs", Ag", Cu(lI),Hg(Il) , Cd(lI)' Sn(ll) , Pb(Il), Bi(Il), Be(Il),Mg(Il), Ca(ll), Ba(Il), Sr(II) , AI(IIl), Mn(II),Cr(IIl), As (III) , Sbfl H, V), Ni(ll) , Co(U) , Zn(II) ,Ga(III), In(IlI) , TI(I), Se(IV, VI), V(V), Au(IIl),Pt(IV), Pd(II) , Ru(III), Rh(III) , Os(VIIl), Ir(IV) ,La(III), Nd(III), Pr(IIl), Gd(III), Sm(III), Y(III),KOTESHf(IV), Zr(JV) , Re(VIl) , W(VI), NO;, NOa, CO~-,ci-, Br-, 1-, SCN-, SO~-, SO;-, S20~-, S20~-, CrO~-,Cr20~-, CIOa,CI04, Br03, to; Fe(CN)~- and Fe(CN)~-.Th(IV), CeCIlI, IV), V(IV), Fe(Il, III), S2- and PO~-ions, however, interfere.The serious interference caused by fluoride,oxalate, citrate, tartrate, and EDTA is obviatedby boiling the test sample three to four times withHN03 to almost dryness followed by evaporationwith water. Interference due to fluoride and EDTAhas also been overcome by treating the sample solu-tion with a mixture of aluminium and nickel ionsin the presence of ammonium acetate and AcOR.During this operation aluminium ions form morestable complex with fluoride ions than uranium ionswhereas nickel ions mask EDTA. The high selec-tivity of the determination of uranyl ions has beenachieved by incorporating arsenate ions as the fixingagent for uranyl ions under the specified conditions.During the determination of arsenic in tobacco,alkaline peroxide method has been preferred overthe conventional wet acid digestion process. Sincethe organic materials (pyridine and other nitrogenring compounds) present in tobacco are hard todecompose, wet oxidation takes very long time witha large consumption of acids. This difficulty hasbeen obviated in the present alkaline peroxidemethod for the decomposition of organic matter.The method has been found highly suitable in thecase of tobacco.Acknowledgements are due to Messrs India TobaccoCompany for supplying the tobacco samples.References1. GOLDSTEIN, G. & STARK, C., Anal. cbim, Acta, 19 (1958),439.2. JUNGREIS, E. & LINABEN-DoR, Anal. chim; Acta, 30(1964), 405.3. JOHRt, K. N., HANDA, A. C. & MEHRA, H. C., Anal. chim,Acta, 57 (1971), 217.4. HANDA, A. C. & JOHRI, K. N., Res. Ind., 16 (1971), 292.5. HANDA, A. C. & JOHRI, K. N., Anal. cbim, "Acta, 59 (1972),· 156.6. WEISZ, H., Microanalysis by the r~ng oven technique (Perga-mon Press, London), 1970.7. BELCHER, R., NUTTEN, A. J. & MACDONALD, A. M. G.,· Quantitative inorganic chemistry (Butterworths, London),· 1970, 251.5-Hydroxy-l,4-naphthaquinone (Juglone), aNew Indicator in Acidimetry & AlkalimetryS. S. SAWHNEY & NARESH C. TREHANDepartment of Chemistry, D.A.V. (Postgraduate) CollegeDehra DunReceived 6 January 1975; accepted 6 May 19755-Hydroxy-1,4-naphthaquinone has been successfullyused in acidimetry and alkalimetry. With ju~lone thepH range for colour change (yellow ~ violet) is 7'8-9·9,thereby rendertng it more suitable for acid-basetitrations as compared to phenolphthalein.NAPHTHAQUINONE and its derivatives havebeen used in industryt, medicines and forqualitative and quantitative estimation of metal29.S'

Selective Microdetermination of Uranium Using Weisz Ring Oven Technique: Application to an Indirect Determination of Trace Amounts of Arsenic in Tobacco

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Selective Microdetermination of Uranium Using Weisz Ring Oven Technique: Application to an Indirect Determination of Trace Amounts of Arsenic in Tobacco

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