ELECTROPHORIC LABELING OF NUCLEOSIDES FOR SENSITIVE ANALYSIS BY NEGATIVE-ION CHEMICAL IONIZATION GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

The formation and analytical utility of several electrophoric derivatives of native and oxidatively modified nucleosides of deoxythymidine and deoxyguanosine were studied. Derivatives include the incorporation of trimethylsilyl, acetyl or perfluoroacyl groups together with pentafluorobenzyl. Acetylation followed by pentafluorobenzylation was the most favourable method. In general, the combined information from the electron impact, positive ion chemical ionization and negative ion chemical ionization spectra was well suited for structure elucidation purposes. The acetyl-pentafluorobenzyl derivative of deoxythymidine was prepared in quantitative yield and was very sensitive on analysis by gas chromatography negative ion chemical ionization. Injection of 0.45 fmol of 3',5'-bis(O-acetyl)-3-pentafluorobenzyl-deoxythymidine, in multiple ion detection experiments, gave a response with a signal-to-noise ratio larger than 10.