DIN EN ISO 13904:2016-06

This International Standard specifies a method for determination of the total and free tryptophan (Trp) content in feeding stuffs (for example, complete and complementary feeds, supplementary feeds, raw materials, ingredients, and concentrates) and determination of free tryptophan in commercial pure substances and premixtures containing more than 2 % of tryptophan. It does not distinguish between D- and L-forms. For the determination of the total tryptophan, the sample is hydrolysed under alkaline conditions with saturated barium hydroxide solution and heated to 110 °C for 20 h. After hydrolysis, an internal standard is added. For the determination of free tryptophan, the sample is extracted under mild acidic conditions in the presence of an internal standard. For commercial pure substances and premixtures containing more than 2 % of tryptophan, it is possible to add the internal standard after the extraction. The tryptophan and the internal standard in the hydrolysate or in the extract are determined by reversed phase C18 HPLC with fluorescence detection. The International Standard has been prepared in ISO/TC 34/SC 10 "Animal feeding stuffs" (secretariat: ISIRI, Iran). The committee responsible for the European Standard is CEN/TC 327 "Animal feeding stuffs - Methods of sampling and analysis" (secretariat: NEN, Netherlands). Working Committee NA 057-03-03 AA "Futtermittel (Spiegelausschuss zu CEN/TC 327)" ("Animal feeding stuffs (Mirror Committee of CEN/TC 327)") at DIN Standards Committee Food and Agricultural Products (NAL) is responsible for the German collaboration.