New extraction systems based on N-vinylcaprolactam are proposed for the extraction of histidine, methionine, and proline for their determination in aqueous media and pharmaceutical preparations. The influence of the phase volume ratio, the nature of the salting-out agent and the composition of N-vinylcaprolactam–N-vinylimidazole and N-vinylcaprolactam–N-vinylformamide copolymers on the quantitative characteristics of amino acid extraction is studied. The regularities of interphase distribution of analytes in water-salt extraction systems with different contents of N-vinylcaprolactam units in copolymers are established. Distribution coefficients and degrees of recovery of amino acids in systems with N-vinylcaprolactam–N-vinylimidazole and N-vinylcaprolactam–N-vinylformamide copolymers in the presence of ammonium sulfate salting-out agent are presented. Copolymers based on N-vinylcaprolactam are used for the efficient extraction of amino acids from pharmaceutical preparations from various manufacturers. Determination of histidine, methionine and proline in the aqueous-salt phase after extraction was performed by a spectrophotometric method based on the intrinsic light absorption of amino acids in the UV region of the spectrum. The developed procedure for the extraction-spectrophotometric determination of amino acids in aqueous media and pharmaceutical preparations, including the extraction of target components from tablet forms using N-vinylcaprolactam copolymers, can be recommended for assessing the quality of pharmaceutical products.
Mokshina et al. (Fri,) studied this question.