In situ Methylation and/or FD-MS: A Comparative Study of Their Usefulness in the Structure Analysis of Highly Polar Metabolites

Abstract

Structure analysis of metabolites, viz. compounds excreted from organisms following biological transformation of pharmaceutically active molecules, is generally performed by spectroscopic means after sufficient enrichment and purification by proper separation techniques. Small sample amounts and/or poor sample purity make NMR, UV- and IR-spectroscopy frequently inapplicable, rendering mass spectrometry the method of choice. The build-up of polarity by formation of –OH, –COOH, –NH, –SH groups and/or conjugation with highly polar endogenous material during metabolism, however, makes electron impact mass spectrometry rapidly inapplicable as chances for pyrolysis increase with polarity of the samples. Therefore additional or complementary techniques, such as derivatisation or field desorption mass spectrometry have to be employed. While various derivatisation methods are well established in mass spectrometry and nowadays almost routine in the study of biomolecules, field desorption has been introduced into this area much more recently.