Influence of fluorine atoms on the electron impact and chemical ionization mass spectrometric fragmentation of methyl x-deoxy-x-fluoro-per-O-methyl-β-D-galactopyranosides

Fully methylated methyl x-deoxy-x-fluoro-β-D -galactopyranosides were studied using electron impact (EI) and chemical ionization (CI) mass spectrometry and by gas chromatography (GC)/mass spectrometry. Metastable daughter- and parent-ion measurements and high-resolution measurements were used to evaluate the fragmentation schemes. Both the presence and the position of the electronegative fluorine atom influences the fragmentation pathways of the permethylated compounds. The individual methyl x-deoxy-x-fluoro-per-O-methyl-β-D - galactopy-ranosides have different GC retention times. This, together with the characteristic differences present in the EI or CI (methane or isobutane) mass spectra, allows the location of fluorine in these substances to be unambiguously determined.