Chemical ionisation mass spectrometry.

Almost all of the work on chemical ionisation (Cl) mass spectrometry, reported to date, has been performed using the high pressure mass spectrometric technique in which the ion source is operated at a pressure of ca. 1 Torr. This work involves the development of an ion source, based on the three-dimensional quadrupole ion trap (QUISTOR), with which it is possible to perform Cl studies at pressures of ca. 10⁻⁵ Torr.

The characteristic features of the chemical ionisation process are first described in general terms and this is followed by a literature review of the instrumental aspects of chemical ionisation mass spectrometry. After a brief theoretical description of the Quistor an account is given of the physical characterisation of the device, which includes a study of the limits of stability and also ion loss and ejection processes.

This is followed by a description of the design, construction and characterisation of a Quistor-type ion source for a magnetic sector mass spectrometer and the use of this instrument to produce low pressure Cl mass spectra. The modification of the same type of mass spectrometer to operate in the high pressure Cl mode is then described, this includes the design and construction of a high pressure ion source and the sample and reagent gas introduction systems. Finally, the performance of the Quistor as a low pressure Cl ion source is compared with that of the high pressure Cl ion source.