Determination of proteinogenous amino acids in feedstuffs, compound feeds, and feed raw materials

INTRODUCTION

The method is used for the determination of the mass fraction of total amino acids: arginine, lysine, tyrosine, phenylalanine, histidine, leucine and iso-leucine (as a sum), methionine, valine, proline, alanine, glycine, cystine, tryptophan, aspartic, and glutamic acids in feedstuffs, compound feeds, fodders, premixes, and all types of feed raw materials by capillary electrophoresis.

The method is intended for the determination of the total content of amino acids in a sample, e.g. the sum of both free and bound forms. Due to the hydrolysis stage of the sample treatment, the aspartic acid and glutamic acid content is the sum of the acid content and its amide (asparagine and glutamine respectively) content. Cystine content represents the sum of cystine and cysteine that are both oxidized to cysteic acid prior to analysis. Leucine and iso-leucine form an unresolved peak thus representing its summary content.

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 determination of hydroxy analogues of amino acids. For the determination of methionine hydroxy analogue (HMTBa) in fodder additives use the method М 04-83-2014 (Lumex Instruments set, order No 0300001888).

MEASURING METHOD

The determination of amino acids in the samples is made either after preliminary alkaline hydrolysis for tryptophan or after acidic hydrolysis for all the other amino acids. Free amino acids are transformed to phenylisothiocyanate derivatives (PITC derivatives) and their ionic forms are determined by capillary zone electrophoresis with direct UV detection at the wavelength of 254 nm. Tryptophan is quantified without derivatization by capillary zone electrophoresis with direct UV detection at the wavelength of 219 nm.