Application of ionic liquids based on imidazole to the electrophoretic determination of amino acids in urine

Abstract

The effects of the ionic liquids C12MImCl and C16MImCl as background electrolyte components on the migration parameters of amino acids under the conditions of capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) were found. It was established that the introduction of the above ionic liquids based on imidazole into a background electrolyte (phosphate buffer solution, pH 2.0) led to an increase in efficiency by a factor of 2–3 in the determination of tryptophan, tyrosine, and 3,4-dihydroxyphenylalanine under the conditions of CZE and in separation selectivity in the MEKC mode. The application of intracapillary concentration (field-amplified sample stacking) with the use of C16MImCl as a background electrolyte constituent made it possible to concentrate tryptophan, tyrosine, and 3,4-dihydroxyphenylalanine by a factor of 10–14. The limits of detection of the amino acids were 30–55 ng/mL. It was found that the inclusion of C12MImCl into the composition of the electrophoretic system makes it possible to determine glycine, which does not absorb in the UV of the region of the spectrum, under the conditions of indirect detection at 220 nm. A procedure was proposed for urine sample preparation for the electrophoretic determination of amino acids with the use of C6MImNTf2 as an extractant. The degrees of amino acid recovery were 92–100%.