Abstract: The method includes the steps of assembling one or more blanks (1) in supporting means (2, 3) so that the or each blank occupies at least the space to be occupied by elongate electrodes and, without disturbing the position of the blanks relative to said supporting means, removing material from all said blanks to generate said electrodes in position in said supporting means. Preferably the material is removed by an electrode-discharge machining (EDM) process, e.g. diesinking. The method avoids time-consuming alignment of preformed electrodes in said supporting means.

Abstract: This invention relates to a method of operating quadrupole mass spectrometers with only an RF potential applied to the filter rods so that the spectrometer operates to pass all ions above a particular value of m/e. In practice, spectrometers operated in this way usually show a marked loss in transmission efficiency for ions of high m/e when operated with an RF potential low enough to pass ions of m/e<10, and the invention overcomes this defect by providing a method of switching the RF potential between two or more values at which ions of different ranges of m/e values are efficiently transmitted, and combining the output signals at each value to give a resultant signal more accurately proportional to the number of ions formed in the source of the spectrometer, irrespective of their m/e values. The invention can be used to improve the accuracy of total pressure measurement using a conventional residual gas analyzing mass spectrometer, eliminating the need for additional pressure gauges.