METHOD AND APPARATUS OF INCREASING DYNAMIC RANGE AND SENSITIVITY OF A MASS SPECTROMETER

This invention is directed to a method and apparatus of increasing the dynamic range and sensitivity of an ion trap mass spectrometer with the use of external ionization. An increased number of sample ions are introduced into the mass spectrometer for mass analysis with the aid of an automatic ion supply control, or feedback, feature. The feedback portion of the invention controls the gating time, and hence the number of sample ions gated into the mass spectrometer, based on previous measurements of the ion content in the mass spectrometer to gate an amount relative to where space charge and saturation begins. A mass filter may also be used between the ion source and the mass spectrometer to improve the signal-to-noise ratio and increase the net processing time. This mass analyzing system may be used with various methods of mass analysis including mass selective instability, resonance ejection, MS/MS, and MS/MS with a supplemental AC field.