A new method has been developed to identify the isomers of amino acids
by derivatization of the corresponding standards with 1-fluoro-2,4-di
nitrophenyl-5-L-alanine amide (Marfey's reagent or FDAA) and analysis
of the diastereomeric derivatives by a liquid chromatography-thermospr
ay mass spectrometry technique. Quantification of the FDAA derivatives
that originate from standards was possible by using L-phenylalanine a
s the internal standard. The procedure was applied to determine the ch
iralities of the amino acids present in some previously uncharacterize
d blue-green algal peptides (microcystins).