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On the basis of the Isolndole formation mechanism In the o-phthalaldehyde/2-mercaptoethanol (OPA/2-ME) derivatization of primary amines and the structure-stability relationships for Isolndoles, an Improved fluorogenic reagent, naphthalene-2,3-dlcarboxaldehyde (NDA) In the presence of cyanide ion (CN ), has been developed. Reaction of NDA/ CN' with primary amines In aqueous media results In the formation of -substKuted 1-cyanobenz[/]lsoindole (CBI) derivatives which have significantly Improved stability compared to the corresponding OPA/2-ME derivatives (for glycine greater than 50-fold Improvement was realized) and have high quantum efficiencies for fluorescence ( , = 0.54 In 60% aqueous acetonitrile for the CBI--propylamine derivative) In solvent systems commonly used In liquid chromatography. Parameters In the NDA/CN' derivatization of alanine are defined (l.e., pH and the reagent component concentrations) and used In the development of a labeling procedure for amino acid mixtures. Gradient elution fractionation of 18 CBI-amino acid derivatives was accomplished In 60 min and permitted detection limits of less than 200 fmol Injected (excitation 246 nm) or 3 pmol Injected (excitation 420 nm). The utility of the reagent In assaying amino acid mixtures resulting from the enzymatic hydrolysis of the peptides Met-enkephalln and glucagon Is demonstrated.

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