Method to reduce measurement bias

A method of mass analysing a single analytical sample is disclosed comprising: i) transmitting different species of ions through a mass spectrometer; ii) sequentially mass analysing, or otherwise detecting, said different species of ions in a particular sequential order; and then iii) repeating steps i) and ii), wherein the sequential order in which said different species of ions are mass analysed, or otherwise detected, is different when step ii) is repeated. The sensitivity with which the mass spectrometer is able to detect ions varies for a period of time, and step ii) and iii) are performed during that period of time.