Effect of phase locking AC and RF voltages for high mass analysis in a quadrupole ion trap mass spectrometer

Experiments on the influence of locking the AC and RF frequency phases on the mass resolution and line position in the mass spectra from a quadrupole ion trap mass spectrometer were carried out at low ejection values of β(z) to investigate the possibility of using this effect for high mass analysis. At n typical mass scan rate of 1000 u/s the improvement for the mass resolution in these experiments did not exceed 10-20% at β(z)=0.25 compared with 200-250% at β(z)=0.5. However, without phase locking, the mass resolution at β(z)=0.25 was about two times higher than that at β(z)=0.5. Thus, the absolute values for the mass resolution observed without phase- locked AC and RF frequencies at β(z)=0.25 were about the same as at β(z)=0.5 with phase locking. This observation was explained by a significant negative contribution to the mass resolution of the ion microoscillations along the trajectory at the fundamental RF frequency which is different for the cases of β(z)=0.25 and β(z)=0.5.