Liquid chromatographic determination of amino acids using a hollow-fiber membrane reactor

A high-performance liquid chromatographic method using a passive hollow-fiber membrane reactor (HFMR) has been developed for the determination of amino acids. This method involves gradient elution of 18 common amino acids on a C18 column using sodium octanesulfonate as an ion-pairing agent, postcolumn derivatization with o-phthalaldehyde and 2-mercaptoethanol (combined with hypochlorite oxidation for the imino acid proline) introduced into the main flow stream using sulfonated and aminated HFMRs immersed in the reagent solutions, and fluorometric detection of derivatives (lambda ex = 340 nm, lambda em = 450 nm). The detection limits of the proposed method were 0.4 to 20 pmol for each amino acid at a signal-to-noise ratio of 3. For 18 amino acids in amounts of 250-2500 pmol, the precisions were on the order of 1.5-4.8% (relative standard deviation, n = 10). The assay of amino acids in a protein hydrolysate sample by the proposed method is also described.