STUDY OF THE PERFORMANCE OF A GROUP OF QUADRUPOLE MASS SPECTROMETERS

Results are presented from a series of experiments that were designed to characterise quadrupole analyzers. Three different analyzers have been studied. The first, typical of the small quadrupoles often used for residual gas analysis, has rods 50 mm long and 6.25 mm in diameter. The second uses rods of similar diameter, but 125 mm long. The third uses rods of diameter 12 mm and length 230 mm. Simple ion sources were used. All had cylindrical ionization regions with external filaments, in a configuration similar to an extractor ion gauge. All were operated under similar conditions. The sensitivity and linearity of the instrument is found to depend in a complex way on the operating conditions of the ion source. The observed behavior is explained qualitatively by the presence of both electronic and ionic space charge in the ion source.