The Research Of AC Signal For Ion Selection

With the the development of the ion trap technology and the wideapplication of mass spectrometry, the selection of the excitation signal becomecrucial. It determines the selection efficiency. So the design of flexible excitationsignal for ion trap system is very significant.Firstly, the excitation signal should have high signal-to-noise ratio, for theion trap system, which means small excitation signal crest factor. Also, theexcitation signal AC should have a smooth amplitude spectrum and uniformtime-domain signal. Stored waveform inverse Fourier transform algorithm is oneof the most widely used method to generate ion excitation signal, the core of thealgorithm is phase modulation. Though comparing the optimal phase modulationwith the linear phase, random phase and the general quadratic phase modulationalgorithm, the optimal quadratic phase modulation is demonstrated to be thetheoretically optimal phase modulation for square excitation spectra. The resultsof the performance is analysed.The Gibb’s effect found in excitation spectra can be suppressed bysmoothing the specified magnitude spectra. In this paper, a simple method isadopted to solve the problem. The ejection signal is also be generated for selectthe ions of interest. In order to improve the efficiency of ion selection, throughdiscussing the smoothing effect of different window functions, the optimalwindow function is selected to eliminate the Gibb’s effect.In order to reduce the crest factor of the excitation signal, this paperintroduce three methods. And the VDO algorithm is selected for signal synthesis.However, the frequency domain amplitude spectrum of VDO algorithm is notsmooth. So it can not be directly used to produce ion trap excitation signal.A new method is presented, which takes the the advantages of VDOalgorithm in reducing crest factor. The new method combines the SWIFTalgorithm with VDO algorithm for SWIFT algorithm generating the basicexcitation signal, and VDO algorithm reducing the crest factor of time domain signal. At last, the results of the performance is analysed.In order to meet the demand of ion trap, RF and DC signal is also generated.At last, NI PCI5421which is controled by the LabVIEW software, outputs theactual signal for ion trap system.