A data independent acquisition method of mass spectrometry for analysing a sample within a mass range of interest, the method being performed within a time period based on a width of a chromatographic peak of the sample as it elutes from a chromatography system and comprising the steps of: ionising the sample to produce a plurality of precursor ions; selecting precursor ions within a mass range of interest to be analysed; performing a plurality of MS1 scans of the precursor ions comprising: separating the precursor ions in the mass range of interest into a plurality of mass sub-ranges, and for each mass sub-range of precursor ions: mass analysing each mass sub-range of precursor ions across respective mass sub-ranges of interest using a Fourier Transform mass analyser, for identification and/or quantitation of the precursor ions in the MS1 domain; and performing a set of MS2 scans in parallel with each MS1 scan, the set of MS2 scans comprising: segmenting each mass sub-range of precursor ions into a plurality of precursor mass segments, each precursor mass segment having a mass range of no greater than 5 amu; wherein for each precursor mass segment: fragmenting the precursor ions within that precursor mass segment; and performing an MS2 scan of the fragmented ions by: forming an ion packet from the fragmented ions; and injecting the ion packet of fragmented ions into a time of flight mass analyser and mass analysing the fragmented ions, the time of flight mass analyser performing the MS2 scans at a frequency of at least 100 Hz,. ionising the sample to produce a plurality of precursor ions; selecting precursor ions within a mass range of interest to be analysed; performing a plurality of MS1 scans of the precursor ions comprising: separating the precursor ions in the mass range of interest into a plurality of mass sub-ranges, and for each mass sub-range of precursor ions: mass analysing each mass sub-range of precursor ions across respective mass sub-ranges of interest using a Fourier Transform mass analyser, for identification and/or quantitation of the precursor ions in the MS1 domain; and performing a set of MS2 scans in parallel with each MS1 scan, the set of MS2 scans comprising: segmenting each mass sub-range of precursor ions into a plurality of precursor mass segments, each precursor mass segment having a mass range of no greater than 5 amu; wherein for each precursor mass segment: fragmenting the precursor ions within that precursor mass segment; and performing an MS2 scan of the fragmented ions by: forming an ion packet from the fragmented ions; and injecting the ion packet of fragmented ions into a time of flight mass analyser and mass analysing the fragmented ions, the time of flight mass analyser performing the MS2 scans at a frequency of at least 100 Hz,. segmenting each mass sub-range of precursor ions into a plurality of precursor mass segments, each precursor mass segment having a mass range of no greater than 5 amu; wherein for each precursor mass segment: fragmenting the precursor ions within that precursor mass segment; and performing an MS2 scan of the fragmented ions by: forming an ion packet from the fragmented ions; and injecting the ion packet of fragmented ions into a time of flight mass analyser and mass analysing the fragmented ions, the time of flight mass analyser performing the MS2 scans at a frequency of at least 100 Hz,. forming an ion packet from the fragmented ions; and injecting the ion packet of fragmented ions into a time of flight mass analyser and mass analysing the fragmented ions, the time of flight mass analyser performing the MS2 scans at a frequency of at least 100 Hz,.