NEGATIVE-ION MASS-SPECTROMETRY IN A COMMERCIAL GAS-CHROMATOGRAPHY ION-TRAP MASS-SPECTROMETER SYSTEM

Commercial gas chromatography quadrupole ion-trap mass spectrometer (GC/ITMS) instruments have been used in a novel way for the study of negative ions formed from perfluorotributyl-amine and polychlorinated biphenyl compounds, Negative ions, formed during a normal electron impact ionization period in which 70 eV electrons were used, were isolated in an ion trap by the application of a negative DC voltage to the ring electrode that caused all positive ions to be ejected from the ion trap; in the subsequent analytical scan, negatives ions were detected with an electron multiplier biased normally so as to detect positive ions, The major negative-ion species detected from FC-43 were m/z 252 to m/z 633; 34 other negative-ion species were detected also, though in low abundance, The observed negative-ion mass range extended from m/z 252 to milt 633, The signal-to-noise ratio of negative-ion mass spectra was enhanced by operation of the GC/MS instrument in GC mode and averaging the mass spectra acquired, In an examination of 3 hexachlorobiphenyl compounds, the molecular anion cluster around m/z 360 for the non-ortho-substituted congener 169 was observed with a signal-to-noise ratio of ca, 20 for 90 pg injected on column: the response for congener 169 was greater than that for congener 156 (mono ortho-substituted) which, in turn, was greater than that for congener 153 (di-ortho-substituted).