High Capacity Electrostatic Ion Trap Mass Spectrometer and its Signal Processing

Apart from the Kingdon trap/Orbitrap, the electrostatic ion trap (EIT) can be built with various form. The traditional electrostatic beam ion trap (EIBT) possesses a limited dynamic range due to the low space charge tolerance as well as low efficiency detection of image charge signal.A planar type of EIT is designed where a rotational symmetrical trapping field is created between two layers of concentric round and ring electrodes. The ions are trapped and oscillating around the centre plane between the electrodes. The oscillatory motion of ion is simulated and the field distribution was optimized to achieve isochronous motion against energy spread in R, z and directions.The recorded image charge signal can baseline resolve ions of 609 and 609.12 Da within 12 ms transient.Traditional Fourier transform to the image charge signal from EIT generates many harmonic components therefore it is not suitable. Using wavelet transform the mixed peaks of different mass and different harmonics can be separated.The WT coefficient for each scale represents a range of mass to charge ratio, and its distribution is subjected to further Fourier transform. The resulted frequency spectrum are less crowded and may be de-convoluted to mass spectrum.Unwanted harmonic peaks can also be eliminated by linear combination of image charge signals from multiple pick-up electrodes. Test with simulated image charge data gives satisfactory result.