APPLICATION BAN OF CERTAIN AZO COLORANTS FOR COMMODITIES - ANALYSIS AND INTERPRETATION OF ANALYTICAL RESULTS

Approximately 60 % of the colourants being used to colour clothes are azo colourants. In Germany the use of azo colourants is banned for the manufacture or treatment of certain commodities, if these azo coloura nts can form carcinogenic amines by cleaving their azo group/s. These amines are listed in the Ordinance of Commodities (Bedarfsgegenstandev erordnung). Analytical methods for the detection of banned azo coloura nts work indirectly by identifying and determining the listed amines f ormed in the course of the analytical procedure of a reductive cleavag e of the azo groups in the azo colourants. The reductive agent ist sod ium dithionite. Comparative studies with selected colourants showed th at the reaction conditions for cleaving the azo groups are of great in fluence on the formation of the amines. In a citrate buffered medium w ith pH 6 as defined in the official method B 82.02-2 according to sect ion 35 of the Foods and Commodities Act (Lebensmittel- und Bedarfsgege nstandegesetz) banned azo colourants generate amounts of listed amines that are similar to the amounts formed in an alkaline medium. Side re actions that were observed under alkaline conditions generating releva nt amounts of amines, originating from other sources as from banned az o colourants, are however suppressed. An exception is the formation of relevant amounts of 4-aminodiphenyl and 2-naphthylamine. In order to avoid misinterpretations with regard to the origin of amines, when the se are formed only in small amounts, a so called threshold value of re cognition or identification was defined by the Working Group ''Analysi s of Banned Azo Colourants'' under section 35 of the Foods and Commodi ties Act. This value is 30 mg amine/kg of product parts of the same ki nd. If the determined concentration of an amine is below this threshol d value, it is not sure that the amine was formed by cleaving an azo g roup. Then further investigations are necessary. The comparability R d etermined in a ring test and helpful to value e. g. the precision of b enzidine analysis performed with the official method B 82.02-2 was R = +/- 39 % for the HPLC determination.