ISO 13903:2005描述了使用氨基酸分析仪或HPLC设备测定饲料中的游离（合成和天然）和总（肽结合和游离）氨基酸。适用于以下氨基酸:半胱氨酸和半胱氨酸的总和；蛋氨酸；赖氨酸；苏氨酸；丙氨酸；精氨酸；天冬氨酸；谷氨酸；甘氨酸；组氨酸；异亮氨酸；亮氨酸；苯丙氨酸；脯氨酸；丝氨酸；酪氨酸；缬氨酸。 该方法不区分氨基酸的盐，也不区分D型和L型氨基酸。 它不适用于色氨酸或氨基酸羟基类似物的测定。 定量限值取决于色谱设备，但最低水平为:0.3 g/kg总赖氨酸；0.25 g/kg总蛋氨酸；0,35 g/kg总半胱氨酸加半胱氨酸；0.2g/kg总苏氨酸；0035g/kg游离赖氨酸；0035g/kg游离蛋氨酸；通常可以分析0,03g/kg游离苏氨酸。

ISO 13903:2005 describes the determination of free (synthetic and natural) and total (peptide-bound and free) amino acids in feeding stuffs, 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, nor does it differentiate between D and L forms of amino acids. It is not valid for the determination of tryptophan or hydroxy analogues of amino acids. Limits of quantification depend on the chromatographic equipment, but levels as low as: 0,3 g/kg total lysine; 0,25 g/kg total methionine; 0,35 g/kg total cystine plus cysteine; 0,2 g/kg total threonine; 0,035g/kg free lysine; 0,035g/kg free methionine; and 0,03g/kg free threonine can typically be analysed.