Ion packet generation for mass spectrometer

Abstract

A method of providing an ion packet to an analyzer section of a mass spectrometer from an ion beam, a pulser which can execute such a method, and a mass spectrometer which includes such a pulser. In the method, a field pulse is applied to extract an ion packet from the beam at a sideways direction to the beam and provide it to a mass analyzer section of the mass spectrometer, which pulse simultaneously causes non-extracted ions of the beam to be deflected onto an electrode of opposite charge. The pulse ON time is significantly longer than conventionally used. For example, the pulse ON time may be longer than the pulse OFF time or at least twice as long as or several times longer than required to extract the ion packet and provide it to the mass analyzer section, so as to reduce stray ions entering the mass analyzer section. Preferably, the pulse ON time is the time required for ions of a predetermined highest mass of interest to be analyzed by the analyzer section, minus the time required to refill the region of the beam from which the ion packet is extracted with ions of the predetermined highest mass. Ion leakage into the mass spectrometer section between packet extractions, and hence detected noise, can be reduced.