HIGH MASS-RESOLUTION USING A QUADRUPOLE ION-TRAP MASS-SPECTROMETER

Modifications have been made to the quadrupole ion-trap mass spectrometer (ITMS) to improve the resolution. An offset-digital-to-analog converter/attenuator network is used to slow down the scan rate in the mass-selective instability mode of operation with resonance ejection. Attenuations of the scan rate by 200 to 700 times increase the resolution from 500 (with no attenuation) to 40 000 and to 100 000 (full width at half maximum), respectively, for the [M + H]+ peak of substance P (m/z 1348). These improved resolutions are achieved in experiments which use resonance ejection to extend the mass-to-charge range.