Amino acid enantiomer separation: GC-MS analysis and signal processing to detect chemical biomarkers in space analysis

This work describes a GC-MS method for enantioselective separation of amino acids: it is based on a derivatization reaction which employs a mixture of alkylchloroformate-alcohol-pyridine, as reagents to obtain the N(O,S)-alkylalkoxycarbonyl esters of amino acids. The aim is to search for a suitable candidate for amino acid separation and quantification in in-situ space GC-MS investigation of solar system body environments onboard space exploration probes. Various reaction parameters are investigated and optimized to achieve a reproducible derivatization procedure of 20 proteinogenic amino acids: the obtained derivatives were submitted to enantiomeric separation on a Chirasil-L-Val chiral capillary column. In particular, the following topics are investigated for i) the proper reagent and reaction conditions to obtain the highest derivative yield; ii) the amino acid reactivity and the MS properties of the obtained derivatives; iii) the linearity and sensitivity of the analytical method; iv) the retention behaviour of the derivatives and their enantiomeric separation. By combining the resolution power of the Chirasil-L-Val column and the high selectivity of the SIM (Single Ion Monitoring) MS detection mode, the described procedure enables the enantiomeric separation and quantification of 16 enantiomeric pairs of amino acids. To extract chemical information from the complex chromatograms obtained, a signal processing method was applied: it’s based on the study of the Experimental AutoCoVariance Function (EACVF) computed on the chromatogram acquired in digitized form. The ACVF method gives informations on the separation performance and the total number of components present in the sample. Moreover, the presence of enantiomeric pairs can be identified and their abundance estimated. The procedure is simple and fast and reproducible. It displays a wide linearity range at ppb detection limits for quantitative determinations for the 20 proteinogenic amino acids investigated.