A commercial quadrupole ion trap GC/MS instrument has been used for the study of negative ions formed from perfluorotributylamine, FC-43. Negative ions formed during electron impact ionization with 70 eV electrons were isolated in an ion trap by the application of a negative DC voltage to the ring electrode; in the subsequent analytical scan, anions were detected with an electron multiplier biased normally so as to detect positive ions. The major anion species detected were m/z 452, 595 and 633; 34 other anion species were detected also, though in low abundance. The observed anion mass range extended from m/z 252 to m/z 633. The signal/noise ratio of anion mass spectra was enhanced by operation of the GC/MS instrument in GC mode and averaging the mass spectra acquired. In another experiment, the molecular anion cluster around m/z 360 for a non-ortho-substituted hexachlorobiphenyl compound, congener 169, was observed with a signal/noise ratio of ca. 20 for 20 pg injected onto column.

An interpretation of these results will be presented, making reference to ion simulations which explore the mass dependence of the ion kinetic energy distributions during mass-selective ion ejection from an ion trap.