The present disclosure provides a mass spectrometer for performing an analysis of sample ions, and a method for operating a mass spectrometer. The mass spectrometer comprises a first ion optical element that is supplied with a first gas; a mass analyser, wherein the performance of the mass analyser is dependent on the pressure of the first gas in the first ion optical element; and a controller for setting a property of the first gas, which comprises at least the pressure of the first gas, on the basis of a characteristic of the analysis to be performed by the mass spectrometer.
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