LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY ANALYSES OF SMALL MOLECULES USING ELECTROSPRAY AND FAST-ATOM-BOMBARDMENT IONIZATION

Electrospray ionization and fast-atom bombardment (FAB) are both soft ionization techniques which typically give prominent molecular ions of thermally labile and highly polar molecules. These two complementary techniques were compared on the same magnetic sector mass spectrometer , a Finnigan MAT 900. Comparisons were made of sensitivity, versatilit y, ease of use, and most importantly for our work, structure elucidati on of unknowns arising from research with agricultural chemicals. Both known standards and 'real world' unknowns were analyzed by liquid chr omatography/mass spectrometry (LC/MS) with both interfaces. The sam re versed-phase micro-LC system was used with both ionization techniques, using 0.32 mm i.d. packed capillary LC columns at flow rates of 1-2 m uL/min. Improved performance in the continuous-flow FAB mode was obtai ned by use of a screen target. The advantages, disadvantages and simil arities of these two ionization techniques are discussed.