A method of mass spectrometry is disclosed comprising separating ions temporally in a first device 5 and analysing the mass or mass to charge ratio of the ions or of product or fragment ions derived from the ions in a mass or mass to charge ratio analyser 8 disposed downstream of the first device 5. The method further comprises obtaining a first set of drift times for the ions through the first device 5 by measuring ion arrival times and determining the transit time of the ions and/or of the product or fragment ions through one or more intermediate regions or devices 6, 7 disposed between the first device 5 and the mass to charge ratio analyser 8. The method further comprises obtaining a second set of drift times for the ions through the first device 5 by correcting the first set of drift times to account for the determined transit times.