Components of scientific analytical equipment. More particularly, ion detectors of the type which incorporate electron multipliers and modifications thereto for extending the operational lifetime or otherwise improving performance. The ion detector may be embodied in the form of a particle detector having one or more electron emissive surfaces and/or an electron collector surface therein, the particle detector being configured such that in operation the environment about the electron emissive surface(s) and/or the electron collector surface is/are different to the environment immediately external to the detector.

A method of determining an expected response to injecting a beam of ions of a species of interest into a static field mass filter of a mass spectrometer including a mass analyser is provided. The method includes: measuring an intensity of ions injected into the static field mass filter for various combinations of test ion species, test magnetic field strengths, and test electric field strengths; determining electric field strengths corresponding to an intensity equal to a first and a second fraction of the measured peak intensity; based on a predetermined relationship between magnetic field strength, electric field strength and centre mass of the static field mass filter, determining mass values corresponding to the determined electric field strengths; and interpolating, from said mass values and for each ion species and for at least one of the test magnetic field strengths, expected mass values for an ion species of interest.