Direct liquid introduction LC/MS microbore experiments for the analysis of nucleoside material present in human urine

In order to obtain detection limits low enough for the analysis of nucleoside material in biological samples, a direct liquid introduction (liquid chromatographic/mass spectrometric DLI) system was upgraded by inserting a self-built desolvation chamber between the DLI probe and the ion source and by switching to microbore high-performance liquid chromatography (HPLC) on a C-18 column. The system was evaluated for the analysis of pure nucleoside and 2'-deoxynucleoside compounds in CH3OH + H2O (80/20) and for the analysis of nucleoside mixtures which were separated using 0.01 M ammonium formate + methanol (97:3) as eluant. The detection of structurally important fragment ions in the lower mass region which could not be observed before and an enhanced sensitivity are considered to be the main improvements. In combination with an appropriate clean-up procedure the system was evaluated for the DLI liquid chromatographic/mass spectrometric analysis of some nucleosides present in a human urine sample. Pseudouridine and 5,6-dihydrouridine were detected and identified.