A catalytic method, based on the iodine-azide reaction, of the determination of sulfide in whole human blood is described. The method involves generation of hydrogen sulfide in an evolution-absorption apparatus by addition of sulfuric acid and subsequent trapping of the generated hydrogen sulfide in sodium hydroxide solution. The catalytic method allows the determination of sulfide without any interference from other sulfur compounds present in blood. A linear calibration graph was obtained over the range 1 x 10(-6)-5 x 10(-4) mol dm-3 sulfide and the proposed method is compared with an ion-selective electrode method.

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Abstract.A new catalytic method for the determination of divalent sulphur compounds, which are soluble or insoluble in water, based on the iodine-azide reaction in various alcoholic solutions is described. As model divalent sulphur catalysts the sodium sulphide and thiourea were chosen. Determination of ethylenethiourea in alcoholic extracts from apples and bananas was an example of practical application of the proposed method. To that purpose five previous elaborated techniques were adopted: titration, volumetric, gas chromatographic, enthalpimetric and potentiometric. The effect of other organic solvents, salts, acids and pH on the determination of divalent sulphur catalysts was also evaluated.Key words: catalysis, tritration, volumetry, enthalpimetry, potentiometry, gas chromatography, divalent sulphur compounds, ethylenethiourea.More than 600 methods of the determination of divalent sulphur compounds based on the catalyzed iodine-azide (i a) reaction in aqueous solution have been develop-S 2 ed and described in literature: 2NaN 3 + 12 ~ 2NaI + 3N 2. The extent of the i-a reaction and, in consequence, the sensitivity of the determination is different for each group of sulphur catalysts in the (-II) oxidation state. Our interest in determining sulphur compounds in mixed medium i~e. aqueous-organic, or non-aqueous medium, i.e. organic solvent or mixture of Organic solvents is connected with the fact that there are many divalent sulphur compounds (ca. 30%) which are insoluble or sparingly soluble in water or those which are decomposed in the first contact with water. Thereby they cannot be determined in aqueous solution. Replacement of

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