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Determination of α-dialkylamino acids and their enantiomers in geological samples by high-performance liquid chromatography after derivatization with a chiral adduct of o-phthaldialdehyde

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Abstract

Derivatization with o-phthaldialdehyde (OPA) and the chiral thiol N-acetyl-l-cysteine (NAC) is a convenient and sensitive technique for the HPLC detection and resolution of protein amino acid enantiomers. The kinetics of the reaction of OPA-NAC with α-dialkylamino acids was investigated. The fluorescence yield of α-dialkylamino acids was only about 10% of that of protein amino acids when the derivatization was carried out at room temperature for 1–2 min, which is the procedure generally used for protein amino acid analyses. The fluorescence yield of α-dialkylamino acids can be enhanced by up to ten-fold when the derivatization reaction time is increased to 15 min at room temperature. The OPA-NAC technique was optimized for the detection and enantiomeric resolution of α-dialkylamino acids in geological samples which contain a large excess of protein amino acids. The estimated detection limit for α-dialkylamino acids is 1–2 pmol, comparable to that for protein amino acids.

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    Present address: Environmental Sciences Program, University of Massachusetts, Boston, MA 02125-3393, USA.

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