Patent ID: 7199363

Claim:
A method of mass spectrometry comprising: providing a Time of Flight mass analyser comprising an ion mirror; maintaining said ion mirror at a first setting; obtaining first time of flight or mass spectral data when said ion mirror is at said first setting; maintaining said ion mirror at a second different setting; obtaining second time of flight or mass spectral data when said ion mirror is at said second setting; determining a first time of flight of first fragment ions having a certain mass or mass to charge ratio when said ion mirror is at said first setting; determining a second different time of flight of first fragment ions having said same certain mass or mass to charge ratio when said ion mirror is at said second setting; and determining from said first and second times of flight either the mass or mass to charge ratio of parent ions which fragmented to produce said first fragment ions and/or the mass or mass to charge ratio of said first fragment ions; and obtaining a parent ion mass spectrum.