Gas Chromatography-Mass Spectrometry of Catecholamines and Tryptamines: Determination of Gas Chromatographic Profiles of the Amines, Their Precursors and Their Metabolites

Abstract

The physiological importance of these substances has recently stimulated a surge of interest in the application of sensitive and specific analytical methods for their determination. In contrast with other reports in the literature, the method presented here concentrates on the development of gas chromatographic and mass spectrometric techniques for the simultaneous assay of complete profiles of catecholamines and tryptamines. The amines and related substances of interest (precursors as well as alcoholic and acidic metabolites) have all been converted to pentafluoropropionyl derivatives for GC analysis. The optimum conditions for derivatization in terms of reaction kinetics and yields have been established. Carboxylic groups of the acidic metabolites have been methylated with BCl₃-methanol. As expected for very polar and labile compounds, significant degradations and quantitative losses have been detected in a few cases. Methods to overcome this problem are discussed. Reproducible quantitative determinations at the nanogram and picogram levels have been obtained with the FID and ECD respectively. For some of the amines the detection limit has been established at five pg. Response curves of several derivatives are presented and the relative FID and ECD response factors of eicosane, lindane, acylated metanephrine and normetanephrine are evaluated and compared. Identification of the derivatives has been accomplished via combined GC-MS, and respective Kováts Retention Index values have been calculated in three of the stationary phases used in this work (SE-30, OV-17, OV-225). Mass spectral data are presented as proof of structural assignments. This work has been carried out using a specially modified GC-MS interface. The results obtained show that it is possible to obtain relatively fast qualitative and quantitative profiles of most of the compounds implicated in the metabolism of tryptophan and phenylalanine via the indole and catecholamine pathways, respectively.