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AssigneeVG Instruments Group Limited
InventorJonathan H. Batey
Estimating the term…
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.
A method of determining the total pressure of a gas mixture present in the source of a quadrupole mass spectrometer having a detector and a mass filter to which only an RF potential is supplied, when the gas mixture contains components from which ions are formed which have maximum transmission efficiencies at different values of said RF potential, the improvement comprising maintaining the RF supply to said mass filter at a first potential at which ions of a first range of m/e values are efficiently transmitted and determining the ion current falling on said detector, and subsequently maintaining said RF supply at one or more further potentials at which ions of one or more further ranges of m/e values are efficiently transmitted and determining the ion current falling on the detector at each of said further potentials, and combining signals indicative of all said ion currents to produce an indication of the total pressure of the said gas mixture.
A method of using a mass spectrometer having a detector and a quadrupole mass filter supplied only with an RF potential to measure the total pressure of the residual gases in a vacuum system, said method comprising:
A mass spectrometer comprising an ion source, a mass filter of the quadrupole type capable of being supplied only with an RF potential so that it simultaneously transmits ions of a wide range of m/e values, and an ion detector arranged to produce a signal indicative of the intensity of the ion beam emerging from said mass filter, said mass filter incorporating means for switching said RF potential between a plurality of values selected so that at each potential ions of different ranges of m/e values are efficiently transmitted, and means for combining the signals from said detector generated at two or more of said selected values of RF potential to produce a signal indicative of the total number of ions generated by said ion source, irrespective of their m/e values.
Dependencies are inferred from the claim text.