ELECTRON MONOCHROMATOR MASS-SPECTROMETER INSTRUMENT FOR NEGATIVE-ION ANALYSIS OF ELECTRONEGATIVE COMPOUNDS

Electron monochromators designed for the production of low energy elec trons (0-15 eV) with nearly monoenergetic distributions have been avai lable for many decades. The concept of adapting the electron monochrom ator as an ion source onto mass spectrometers for the purpose of elect ron capture negative ion-mass spectrometric (EM-MS) analyses is only n ow being realized. Two different analyzers, a quadrupole and a double focusing sector instrument, have recently been retrofitted with electr on monochromators to test their utility as analytical instruments for the detection of environmental compounds and chemical agents. Electron energy scans of compounds in these classes reveal unique negative ion resonances, which can be used as an additional analytical dimension o f information for compound identification and confirmation. Electron c urrents of 430 mu A at 0.03 eV electron energy are now available from the electron monochromator, which will provide sufficient electron flu x to meet modern standards for trace level analyses. The narrowest ele ctron energy spread achieved has been +/-0.07 eV (fwhm). The electron monochromator-mass spectrometer (EM-MS) instrument has been interfaced to a gas chromatograph (GC), and this system (GC/EM-MS) was used to r ecord ion chromatograms of mixtures of polychlorinated compounds. Regi oselective ion loss, resulting from dissociative electron capture by t he parent molecule, is electron-energy dependent and can be monitored with the EM-MS instrument. Finally, positive ion spectra produced with monoenergetic electrons have also been recorded. (C) 1997 John Wiley & Sons, Inc.