Applicability of fast-atom bombardment mass spectrometry to the characterization of fulvic acid Original Research Article

A variety of experimental parameters have been evaluated for their effect on the fast-atom bombardment (FAB) mass spectrum of five fulvic acids. Eleven common FAB matrices were evaluated. Only glycerol gave any indication of a fulvic acid spectrum, and this was a very weak signal increase superimposed onto the glycerol spectrum. Continuous-flow FAB was also evaluated using a glycerol matrix and no significant signal was observed in the FAB mass spectrum. Five techniques used to modify the matrix or the sample to enhance a spectrumʹs signal-to-noise ratio were also studied. Surfactants were added to modify the matrix surface tension, removal of sodium from the fulvic acid samples (to minimize the formation of ([M + Na]+) was accomplished using complexation and ultra-centrifugation, fulvic acid `ionsʹ were preformed in the matrix by the addition of acid or base, and fulvic acid was methylated to increase its hydrophobicity. None of these techniques enhanced the FAB mass spectrum of fulvic acid. The lack of a significant ion intensity attributable to fulvic acid is probably due to its heterogeneous, multi-component nature. Despite some reports in the literature to the contrary, it does not appear that it is possible to characterize fulvic acid by FAB mass spectrometry.