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A new reaction for determining iodate in table salt is proposed. It is based on oxidation of phenylhy-drazine-4-sulfonic acid by iodate in acidic medium to the 4-diazobenzenesulfonic acid cation and its electrophilic coupling with N-(1-naphthyl)ethylene- diamine dihydrochloride to give an azo dye, which is measured spectrophotometrically at 545 nm. Maximum molar absorptivity was 8.41 ×104 L/mol cm. A rectilinear calibration graph was obtained for iodate in the range 0.25–5 mg/L. The azo dye could be preconcentrated at least 40-fold by solid-phase extraction on C18 sorbent. The limit of detection was 0.6 μg iodate/L. The method was used to determine iodate in laboratory-prepared and commercially available table salt samples. Up to 5 mg bromate/kg and 10 mg iron(lll)/kg in table salt did not interfere.

Ascorbic acid is frequently determined by titration with 2,6-dichlorophenolindophenol. The determination is rapid, but the method is neither specific for ascorbic acid nor very sensitive. The coloring matter in the assay solution interferes with the visual endpoint, and iron(ll), copper(l), sulfite, and sulfhydryl substances such as cysteine and glutathione interfere with the color reaction. Sample cleanup by solid-phase extraction with C18 bonded silica was developed to remove the coloring matter. Extraction sorbent impregnated with 2,2′-bipyridyl, 2,9-dimethyl-1,10-phenanthroline (neocuproine) and Jv-ethylmaleimide removes Fe(ll), Cu(l), and sulfhydryl compounds, respectively. The procedure was applied to highly colored multivitamin pharmaceuticals, soft drinks, and fruit and vegetable juices. In contrast to the results from the original method, which is not applicable to such samples, the results obtained by the method incorporating cleanup were accurate and selective for ascorbic acid. The sample cleanup also permitted determination of dehydroascorbic acid by reducing it to ascorbic acid with cysteine and titrating the ascorbic acid formed with indophenol. As little as 3 μg ascorbic acid was determined by the method incorporating cleanup.

2,4-Dinitrophenylhydrazine has been suggested as a new reagent for the flow-injection spectrophotometric determination of residual chlorine based on its oxidation to 2,4-dinitrophenyldiazonium ion. The measurement of the decrease in colour intensity under reversed flow-injection (reagent injection) conditions has been used for the determination of 0.1–10 mg/l Cl present as free or combined chlorine, and for its speciation. The limit of detection was 0.05 mg/l Cl. Copper (II), iron (III) and many other ions have been found not to vitiate the results.

Department of Chemistry, University of Jabalpur, Jabalpur-482001 Manuscript received 2 November 1976, revised I March 1977, accepted 27 April 1977 Procedures are evolved for the determination of some sulphur containing functional groups. o-Diacetoxy iodobenzoate is proposed and used as an analytical reagent for the determination of mercaptans, thioureas, organic sulphides, disulphides in dilute acetic acid medium and organic derivatives of dithiocarbonic acid at pH 7. The accuracy of the determination of mercaptans is 0.2%, of thioureas 0.5%, organic sulphides and disulphides 0.4%, and of organic derivatives of dithiocarbonic acid 0.5%. All the four methods are precise to 0.2-0.5%.

Department of Chemistry, Government Science College, University of Jabalpur, Jabalpur 482001. Manuscript received 3 November 1976, revised 11 April 1977, accepted 16 April 1977 Titrimetric Determination of Copper(ll) with thioglycollic Acid.

Department of Chemistry, University of Jabalpur, Jabalpur Manuscript received 8 September 1973; accepted 27 August 1974 Procedures are given for the accurate and rapid determination of cysteine, xanthates, and dithio-carbamates in aqueous solutions by titration with mercuric chloride, employing diphenyl­carbazone as the indicator. Carbon disulfide is also estimated by quantitative conversion to xanthate and titration of the latter. Results were reproducible within 0.3% and accurate to 0.5% for the titration of xanthates and dithiocarbamates and 2% low when cysteine was being deter­mined.

Department of Post.Graduate Studies and Research in Chemistry, University of Jabalpur, Jabalpur, (M.P.) Manuscript received 30 December 1972; accepted 17 February 1973 Determination of 3-Mercaptopropionic, Mercaptosuccinic and o-Mercaptobenzoic Acid by Lead Tetraacetate

Department of Chemistry, University of Jabalpur, Jabalpur Manuscript received 17 April 1973; accepted 18 July 1973 A titrimetric procedure is described for determining organic disulfides and sulfides by oxida­tion with phenyliodosoacetate in dilate acetic acid. By applying a second method, sulfides and disulfides can be determined in presence of each other. Mercaptans, if present, can also be deter­mined. The procedure is precise to about ± 0.4%.

Department of Chemistry, University of Jabalpur, Jabalpur Manuscript received 9 March 1973; accepted 18 July 1973 A visual non-aqueous titrimetric procedure for the determination of phenyl and meta or pare substituted phenyl thioureas by lead tetraacetate is described. The method is accurate to about ±0.5% and can be used for routine analysis of phenylthioureas.

Iodine monochloride oxidizes thioureas to respective urea and sulfate in hydrogencarbonate medium. The iodine formed in the reaction is titrated with iodine trichloride to an Andrews end-point. This method has been applied to determine isothiocyanates and amines by their conversion to thioureas.

Procedure. Take an aliquot of sample dissolved in water or dimethylformamide containing 0.1-0.3 meq of mercaptan in a 150-ml Erlenmeyer flask. Add 25 ml of water, 1 g of potassium iodide and 1 ml of 1 ~ starch solution. Titrate with 0.02 M solution of cupric sulphate taken in a 10-ml burette (graduated at 0.02 ml). Shake the solution vigorously during titration. At the end point a blue colour is formed. Under the described conditions of titration no cuprous mercaptide is formed. Cuprous iodide precipitates during the course of titration.