Part of the mass spectrometer that separates the ions according to their m/z ratio. Once ions have been formed and introduced into the vacuum, they are subjected to electrical (DC  and/or RF) or magnetic fields. Their motion under these conditions is a function of many parameters but all include the mass-to-charge ratio. Ions can be ejected from the analyser one m/z at a time (sequential mass analyzer) or can be detected and measured simultaneously.