Sequential injection chromatography for fluorimetric determination of intracellular amino acids in marine microalgae

This chapter describes a sequential injection chromatography method to automate the fluorimetric determination of amino acids after precolumn derivatization with o-phthaldialdehyde in presence of 2-mercaptoethanol using reverse-phase liquid chromatography in C(18) silica-based monolithic column. The method is low-priced and based on six steps of isocratic elutions. At a flow rate of 30 μl/s, a 25 mm long-column coupled to 5-mm guard column is capable to separate aspartic acid (Asp), glutamic acid (Glu), asparagine (Asn), serine (Ser), glycine (Gly), threonine (Thr), citrulline (Ctr), arginine (Arg), alanine (Ala), tyrosine (Tyr), phenylalanine (Phe), ornithine (Orn), and lysine (Lys). Under these conditions, histidine (His) and glutamine (Gln), methionine (Met) and valine (Val), and isoleucine (Ile) and leucine (Leu) coelute. The entire cycle of amino acids derivatization, chromatographic separation, and column conditioning at the end of separation lasts 16 min. The method was successfully applied to the determination of the major intracellular free amino acids in the marine green alga Tetraselmis gracilis.