INFLUENCE OF FLUORINE-ATOMS ON THE ELECTRON-IMPACT AND CHEMICAL-IONIZATION MASS-SPECTROMETRIC FRAGMENTATION OF XY-X-FLUORO-PER-O-METHYL-BETA-D-GALACTOPYRANOSIDES

Fully methylated methyl x-deoxy-x-fluoro-beta-D-galactopyranosides wer e studied using electron impact (EI) and chemical ionization (CI) mass spectrometry and by gas chromatography (GC)/mass spectrometry. Metast able daughter- and parent-ion measurements and high-resolution measure ments were used to evaluate the fragmentation schemes. Both the presen ce and the position of the electronegative fluorine atom influences th e fragmentation pathways of the permethylated compounds. The individua l methyl xy-x-fluoro-per-O-methyl-beta-D-galactopyranosides have diffe rent GC retention times. This, together with the characteristic differ ences present in the EI or CI (methane or isobutane) mass spectra, all ows the location of fluorine in these substances to be unambiguously d etermined.