A method of mass spectrometry is disclosed comprising separating ions temporally in a first device 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 disposed downstream of the first device. The method further comprises obtaining a first set of drift times for the ions through the first device 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 disposed between the first device and the mass to charge ratio analyser. The method further comprises obtaining a second set of drift times for the ions through the first device by correcting the first set of drift times to account for the determined transit times.