Application of the iodine-azide reaction to the catalytic determination of divalent sulphur compounds in alcoholic medium: Determination of ethylenethiourea in some biological materials

Abstract

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

Determination of ETU in Tomatoes and Tomato Products by HPLC-PDA. Evaluation of Cleanup Procedures

“…Recently, there is a clear trend toward the application of the HPLC technique coupled with UV (17)(18)(19)(20)(21), MS (22,23), or electrochemical detection (24)(25)(26). Alternative techniques have been used such as the flow injection spectrofluorometric detection (27) or kinetic method (28) based on the catalytic or inhibitory properties of ETU to certain reactions. These, however, suffer from low selectivity.…”

Determination of Ethylenethiourea (ETU) at Trace Levels in Water Samples by Cathodic Stripping Voltammetry

“…HPLC has been reported to have advantages over the more widely used GC techniques in the determination of ETU, because derivatization procedures can be omitted [15]. Alternative techniques have been used such as the micellar electrokinetic capillary chromatography [16], spectrofluorimetry [17,18] and kinetic methods [19] based on the catalytic or inhibitory properties of ETU to certain reactions. These, however, suffer from low selectivity.…”