The determination of amino-acid enantiomers in human saliva with Chirasil-Val

Abstract

The use of polysiloxanes as stationary phase in glass-capillary gas-chromatography carrying chiral groups enables the separation and quantitation of most amino-acid enantiomers and a variety of other compounds in a much shorter time than previously. This phase exhibits low volatility and high thermal stability and may be used in routine analysis with open tubular columns at temperatures of at least 175 °C. Most protein amino acids are separated in a temperature programme between 90 and 175 °C, thus obviating the need for multiple injections. Resolution factors are lower than those of other diamide phases containing the l-valine-t. butyl-amide group, but are sufficient for resolution of almost all protein amino-acid enantiomers. Incomplete recovery from the sample, incomplete derivatization, hydrolysis and thermal decomposition of the derivative and shifting response factors can be compensated for by adding the unnatural enantiomer. The accuracy of amino-acid analysis by enantiomer labelling is equal or superior to that of known methods and permits complete analysis of peptides with respect to both amino-acid composition and the optical purity of each amino acid. The application of this method to human saliva provided information concerning enzymic and bacterial process in the mouth.