Mass spectrometer having improved quadrupole robustness

Abstract

A method of operating a mass spectrometer, comprising: generating ions from a sample; mass filtering the ions using a quadrupole mass filter having a set of selection parameters to transmit ions within at least one selected range of mass-to-charge ratios narrower than an initial range, wherein the quadrupole comprises four parallel elongate electrodes arranged in opposing pairs to which are applied RF and DC, wherein an attractive DC voltage is applied to one pair of opposing electrodes and a repulsive DC voltage is applied to the other pair; mass analysing or detecting the ions transmitted by the quadrupole mass filter; repeating the steps of generating ions, mass filtering and mass analysing or detecting multiple times; switching a configuration of the pairs of opposing electrodes to which the attractive DC voltage and the repulsive DC voltage are applied multiple times over the course of repeating the steps so that over long term operation the build-up of contamination on each pair of opposing electrodes is substantially equal; and determining mass filtering steps for which quantitative accuracy should be maintained between them and for the determined mass filtering steps maintaining the same configuration of the pairs of opposing electrodes to which the attractive DC voltage and the repulsive DC voltage are applied. The width of the selected mass range may change by not more than 10% when the ion transmission efficiency mass filter falls by 50% or more due to the build-up of contamination on the electrodes.