Patent ID: 6380666
Filing Date: 2002-04-30
Classification: H01J

Abstract:
A time-of-flight mass spectrometer comprising a quadrupole ion trap as an ion source, an ion detector and a field-free drift space between the quadrupole ion trap and the ion source, the quadrupole ion trap having a ring electrode and two end-cap electrodes, at least one of the end-cap electrodes having at least one hole at its centre through which ions can be extracted in use, and voltage supply means for supplying to said at least one end-cap electrode a first extraction voltage relative to said ring electrode and for supplying to another said end-cap electrode a second extraction voltage relative to said ring electrode having the opposite polarity to said first extraction voltage, said first and second extraction voltages being respectively negative and positive voltages for positive ion extraction and being respectively positive and negative voltages for negative ion extraction, the second extraction voltage having a magnitude in the range from 0.5 to 0.8 of that of said first extraction voltage.