This standard describes the determination of free (synthetic and natural) and total (peptide bound and free) amino acids in feedingstuffs, using an amino acid analyser or HPLC equipment. It is applicable to the following amino acids: - sum of cystine and cysteine; - methionine; - lysine; - threonine; - alanine; - arginine; - aspartic acid; - glutamic acid; - glycine; - histidine; - isoleucine; - leucine; - phenylalanine; - proline; - serine; - tyrosine; - valine. The method does not distinguish between the salts of amino acids and it cannot differentiate between D and L forms of amino acids. It is not valid for the determination of tryptophan or hydroxy analogues of amino acids.