METHOD FOR SELECTIVE DETERMINATION OF TRYPTOPHAN AND PHENYLALANINE IN AQUEOUS SOLUTIONS

FIELD: analytical chemistry of organic compounds, possibly standard analysis at production of pharmaceutical preparations such as biologically active food supplements, amino acid mixtures, vitamin complexes. ^ SUBSTANCE: method comprises steps of preparing aqueous solution of tryptophan and phenylalanine at initial concentration 0.05 and 0.02 mg/ml respectively; adding to prepared solution salting out agent -crystalline lithium sulfate till its content 25 mass% in relation to mass of aqueous solution of amino acids; adding to prepared aqueous -salt solution of tryptophan and phenylalanine extragent - three-component mixture of hydrophilic solvents at volume relation of aqueous-salt solution and extragent mixture 10 : 1; preparing mixture of hydrophilic solvents from 60-70 mass% of butyl alcohol, 20 -25 mass% of acetone and 5 -20 mass % of ethyl acetate; then extracting it in vibration mixer for 5 min; curing for several minutes until complete separation of phases; transferring extract to cell for conductometric titration and determining in extract content of tryptophan and phenylalanine. In order to realize it curve is plotted according to result of titration determining relationship of electrical conductivity of solution upon volume of added titrant; detecting with use of fixed points of equivalence mass of tryptophan and phenylalanine in extract. Extraction degree of tryptophan and phenylalanine is calculated with use of formula: R = D - 100/D + r, where D -coefficient of distribution of tryptophan and phenylalanine between three-component mixture of hydrophilic solvents and aqueous-salt solution; r - relation of volumes of aqueous and organic phases. Method allows determine up to 97 =98% of tryptophan and 98 -99% of phenylalanine. ^ EFFECT: enhanced efficiency of selective determination of tryptophan and phenylalanine in aqueous solution. ^ 2 notes, 1 tbl