Electron monochromator mass spectrometry far the analysis of whole bacteria and bacterial spores

Spares from a variety of Bacillus species were analyzed with direct probe m ass spectrometry using an electron monochromator to select electrons of dis tinct energies for ionization. Electron energies were chosen to match the e lectron capture energies of taxonomically important compounds such as dipic olinic acid and fatty acids. Previous negative ion interferences were not o bserved when the monochromator was used, and the signal-to-noise ratio of t argeted compounds was significantly enhanced using this approach. To demons trate the selectivity of the technique, the monochromator was swept over a range of electron energies while monitoring the masses of compounds with kn own electron capture energies. Scanning the monochromator while the mass sp ectrometer was operated in single-ion mode enabled dipicolinic acid to be d etected in 10(5) spores. The results presented here demonstrate the utility of the electron monochromator for selectively ionizing compounds directly in bacteria and bacterial spores.