Modification of High Resolution Mass Spectrometer for Chemical Ionization Studies

Abstract

The additional instrumentation and several modifications required to permit operation of a Consolidated 21–110B mass spectrometer at source pressures of the order of 1 Torr are described. A spark suppressor system was devised to permit operation of the ion source at potentials to 10 kV while the sample handling and pressure measuring equipment are maintained at ground potential. Several circuit modifications necessary for high pressure operation are also described. All changes are compatible with the use of standard components for sample manipulation and with the consecutive use of the ion source for low pressure electron impact and high pressure chemical ionization mass spectroscopy. A resolving power M/ΔM of 56 700 is demonstrated for the instrument, illustrating that the performance is not degraded by high pressure operation. The sensitivity and quantitative accuracy already achieved are comparable to conventional electron impact spectroscopy, while the spectra themselves are greatly simplified.