Applications of gas chromatography and mass spectrometry in neurochemical studies: determination of indole amine profiles at the picogram level.

Work is presented on the application of sensitive and specific analytical methods for the simultaneous assay of tryptophan and its indolic metabolites (5-hydroxytryptophan, serotonin, 5-hydroxy-indole-acetic acid, tryptamine and indoleacetic acid). Due to their small concentrations in selected areas of the central nervous system, suitable derivatives have been prepared for separation by Gas Chromatography (GC) and detection by electron capture (ECD). Carboxylic acid groups have been methylated with BCl3-methanol and phenolic and amine groups have been acylated to pentafluoropropionyl derivatives. This type of derivatives allow a detectability limit of 5 picograms (5 x 10(-12) gr) if the corresponding reaction kinetics and yields are properly optimized. Response curves are presented. Identifications have been obtained by combined GC-MS and by the use of Kovats indeces in two GC stationary phases. The GC separation of the six compounds indicated above can be performed in less than 5 minutes with quantitative reproducibility. This work opens the possibility of performing comparative studies ("screening") of various physiological and pathological conditions by detecting any changes in the profile representative of a whole metabolic pathway, such as that of the indolic compounds in this case.