Tailored excitation for trapped ion mass spectrometry

摘要

An ion cyclotron resonance cell has applied thereto an excitation which has a time domain waveform which is the inverse Fourier transform of a frequency domain excitation spectrum which has been chosen by the user to yield selective excitation and/or suppression of ranges of ion mass-to-charge ratios. To minimize the dynamic range of the time domain signal resulting from the inverse Fourier transform, the phases of the various discrete frequency components in the frequency domain spectrum which are used in calculating the inverse Fourier transform are not constant but rather are varied as a function of the frequency of the components. The phase of each component is assigned such that the frequency components in the time domain signal are not all in phase at any point in time, thereby avoiding large magnitude spikes in the time domain waveform. The phases of the various frequency components may follow a non-linear function of the frequencies of the components, such as a quadratic function. By varying phase in this manner, the time domain signal which is applied to the excitation plates of the ion cyclotron resonance cell has a frequency domain power spectrum which is substantially flat over the specified band or bands of frequencies of interest. The time domain waveform may be shifted and/or weighted before being applied to the excitation plates. Tailored excitation may also be applied in this manner to the end plates of an ion trap cell to cause tailored ejection of specific bands or ranges of ions with retention of remaining ions within the cell.