Daishima, S; Iida, Y; Hamada, S
Four reagent gases, oxygen, methane, isobutane and ammonia, were investigated in chemical ionization mass spectrometry using Townsend discharge (TD). The discharge in oxygen, methane, isobutane and ammonia was initiated the ionization chamber pressure of 0.19,0.45,0.31 and 0. 38 Torr, respectively. In oxygea, extremely stable discharge was observed at a wide range. Oxygen generated efficiently oxide ions (O+, O-) and superoxide ions (O2+, O2-) in the positive and negative ion mode, respectively. In methane, the stable discharge region was dependent on the ionization chamber pressure and discharge voltage, and it was devided into two sections. The composition of the reactant ions was somewhat different from the one of the filament mode, in that the relative ion abundance of C2H5+ in TD mode was larger than the one of the filament mode, and a small amount of C4H7+ and C4H9+ were generated in the TD mode. In isobutane, the stable discharge region was very narrow. The composition of the reactant ions was almost the same as the one of the filament mode. In ammonia, the feature of the stable discharge region was similar to the one in the case of methane. The ion species were the same as those generated in the filament mode, but the relative intensity ratio was different from each other. The repeata-bilities of positive and negative ion chemical ionization mass spectra of perfluorotributylamine and decafluorotriphenylphosphine in TD mode using methane reagent gas were almost the same as those of the filament mode. The calibration graph of benzo[a]pyrene in the range of 0~150 pg using benzo[a]pyrene-d12 as an internal standard in methane reagent gas showed good linearity with correlation coefficient of 0.9999. © 1987, The Chemical Society of Japan. All rights reserved.
