A method of mass spectrometry comprising: ionising a sample eluting from a separation device in order to generate a plurality of parent ions; and performing multiple cycles of operation as said sample elutes from said separation device, wherein each cycle of operation comprises the steps of: (i) mass analysing said parent ions to obtain parent ion mass spectral data; (ii) transmitting said parent ions to a fragmentation or reaction device without substantially mass filtering said parent ions, causing said parent ions to fragment or react to form fragment or product ions and obtaining fragment or product ion mass spectral data; (iii) mass filtering said parent ions so that first parent ions having mass to charge ratios within a first mass to charge ratio range are onwardly transmitted to a fragmentation or reaction device, causing said first parent ions to fragment or react to form first fragment or product ions and obtaining first fragment or product ion mass spectral data; and (iv) mass filtering said parent ions so that second parent ions having mass to charge ratios within a second different mass to charge ratio range are onwardly transmitted to a fragmentation or reaction device, causing said second parent ions to fragment or react to form second fragment or product ions and obtaining second fragment or product ion mass spectral data; characterised in that step (i) further comprises separating parent ions according to their ion mobility and step (ii) further comprises separating fragment or product ions according to their ion mobility; and in that the method further comprises: intersecting mass resolved fragment or product ions from said first and/or second fragment or product ion mass spectral data with time and ion mobility drift time resolved fragment or product ions from said fragment or product ion mass spectral data, retaining only the ions in common, and determining the intensity of fragment or product ions having a particular mass to charge ratio by summing the intensity of said fragment or product ions from said fragment or product ion mass spectral data and said first fragment or product ion mass spectral data and/or said second fragment or product ion mass spectral data. ionising a sample eluting from a separation device in order to generate a plurality of parent ions; and performing multiple cycles of operation as said sample elutes from said separation device, wherein each cycle of operation comprises the steps of: (i) mass analysing said parent ions to obtain parent ion mass spectral data; (ii) transmitting said parent ions to a fragmentation or reaction device without substantially mass filtering said parent ions, causing said parent ions to fragment or react to form fragment or product ions and obtaining fragment or product ion mass spectral data; (iii) mass filtering said parent ions so that first parent ions having mass to charge ratios within a first mass to charge ratio range are onwardly transmitted to a fragmentation or reaction device, causing said first parent ions to fragment or react to form first fragment or product ions and obtaining first fragment or product ion mass spectral data; and (iv) mass filtering said parent ions so that second parent ions having mass to charge ratios within a second different mass to charge ratio range are onwardly transmitted to a fragmentation or reaction device, causing said second parent ions to fragment or react to form second fragment or product ions and obtaining second fragment or product ion mass spectral data; (i) mass analysing said parent ions to obtain parent ion mass spectral data; (ii) transmitting said parent ions to a fragmentation or reaction device without substantially mass filtering said parent ions, causing said parent ions to fragment or react to form fragment or product ions and obtaining fragment or product ion mass spectral data; (iii) mass filtering said parent ions so that first parent ions having mass to charge ratios within a first mass to charge ratio range are onwardly transmitted to a fragmentation or reaction device, causing said first parent ions to fragment or react to form first fragment or product ions and obtaining first fragment or product ion mass spectral data; and (iv) mass filtering said parent ions so that second parent ions having mass to charge ratios within a second different mass to charge ratio range are onwardly transmitted to a fragmentation or reaction device, causing said second parent ions to fragment or react to form second fragment or product ions and obtaining second fragment or product ion mass spectral data; characterised in that step (i) further comprises separating parent ions according to their ion mobility and step (ii) further comprises separating fragment or product ions according to their ion mobility; and in that the method further comprises: intersecting mass resolved fragment or product ions from said first and/or second fragment or product ion mass spectral data with time and ion mobility drift time resolved fragment or product ions from said fragment or product ion mass spectral data, retaining only the ions in common, and determining the intensity of fragment or product ions having a particular mass to charge ratio by summing the intensity of said fragment or product ions from said fragment or product ion mass spectral data and said first fragment or product ion mass spectral data and/or said second fragment or product ion mass spectral data.