DIN EN ISO 17180:2013-08

This standard specifies a method for the quantitative determination of free (non-proteinbound) lysine, methionine, and threonine in commercial products and premixtures containing more than about 10 % mass fraction of the respective amino acid. It does not distinguish between d- and l-forms. The samples are treated in dilute hydrochloric acid and then diluted with sodium citrate buffer. Norleucine internal standard is added and the amino acids are separated by an amino acid analyser or high performance liquid chromatography (HPLC), using a cation exchange resin and sodium citrate buffer eluent solutions. The amino acids are measured colourimetrically following post-column reaction with ninhydrin reagent or by fluorescence detection after post-column reaction with ortho-phthaldialdehyde (OPA). 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). Collaboration of DIN for the field of responsibility of CEN/TC 327 is performed through the national mirror committee, Working Committee NA 057-03-03 AA "Futtermittel" ("Animal feeding stuffs") of NAL.