Method and apparatus for providing tailored excitation as in Fourier transform mass spectrometry
First Claim
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1. Mass spectrometry apparatus comprising:
- (a) an ion trap including a plurality of electrode plates;
(b) means for detecting motion of ions in the trap and providing a signal indicative thereof;
(c) excitation means connected to the ion trap for producing an electric field in the trap, wherein the excitation means generates a sine wave signal at a selected frequency and a sinc function signal of a selected width and center time and multiplies the two signals to provide an excitation signal which is applied to plates of the ion trap, whereby the magnitude spectrum of the excitation signal in the frequency domain is a substantially rectangular function centered on the frequency of the sine wave signal and having a width determined by the width of the sinc function signal.
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Abstract
Tailored excitation of ions in a mass spectrometer is obtained by using an excitation signal which comprises at least one signal having the form of a sinc function modulated sine wave. The sinc modulated sine wave has a magnitude function in the frequency domain in the form of a rectangular function centered at the frequency of the sine wave and having a width determined by the width of the sinc function. Plural sinc modulated sine wave signals can be applied to the ion trap of the spectrometer, with the various signals having different sine wave frequencies, to provide a tailored excitation spectrum without the need for extended computation.
64 Citations
44 Claims
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1. Mass spectrometry apparatus comprising:
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(a) an ion trap including a plurality of electrode plates; (b) means for detecting motion of ions in the trap and providing a signal indicative thereof; (c) excitation means connected to the ion trap for producing an electric field in the trap, wherein the excitation means generates a sine wave signal at a selected frequency and a sinc function signal of a selected width and center time and multiplies the two signals to provide an excitation signal which is applied to plates of the ion trap, whereby the magnitude spectrum of the excitation signal in the frequency domain is a substantially rectangular function centered on the frequency of the sine wave signal and having a width determined by the width of the sinc function signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 39, 40, 41)
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9. Mass spectrometry apparatus comprising:
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(a) an ion trap including a plurality of electrode plates; (b) means for detecting motion of ions in the trap and providing a signal indicative thereof; (c) excitation means connected to the ion trap for producing an electric field in the trap, the excitation means including; (1) sinc function digital memory storing digital data in locations which can be sequentially read out to provide an output signal wherein the data when read out follows a sinc function; (2) sine function digital memory storing digital data in locations which can be sequentially read out to provide an output signal wherein the data when read out follows a sine function; (3) multiplying means for multiplying the output signal of the sinc function digital memory with the output signal of the sine function digital memory to provide a digital output signal; (4) a digital-to-analog converter connected to receive digital data input from the multiplying means and connected to provide its analog output signal to the ion trap; (5) means for selectively controlling the output of digital data stored in the sinc function and sine function digital memories to the multiplying means to apply a desired time domain excitation signal to the ion trap. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. In an ion cyclotron resonance mass spectrometer apparatus of the type having an ion cyclotron resonance trap cell including excitation plates and detection plates, a magnet producing a substantially constant unidirectional magnetic field through the ion cyclotron resonance cell such that the electric field from potentials applied to the excitation plates is transverse to the applied magnetic field, means connected to the detector plates of the cell for detecting resonance motion of ions in the cell and providing a signal indicative thereof, and an excitation amplifier connected to the excitation plates for applying electrical potentials to the plates to form an electric field between the plates in accordance with the input signal to the excitation amplifier means, the improvement comprising:
excitation generator means connected to the excitation amplifier for providing an excitation signal to the amplifier, wherein the excitation generator generates a sine wave signal at a selected frequency and a sinc function signal of a selected width and center time and multiplies the two signals to provide the excitation signal, whereby the magnitude spectrum of the excitation signal in the frequency domain is a substantially rectangular function centered on the frequency of the sine wave signal and having a width determined by the width of the sinc function signal. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23)
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24. A method of providing tailored excitation to a spectrometer having excitation electrodes, comprising the steps of:
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(a) generating a sine wave signal of a selected frequency; (b) generating a sinc function signal of a selected width and center time; (c) multiplying the sinc function signal and the sine function signal to provide a time varying excitation signal; and (d) applying the excitation signal to the excitation electrodes whereby a time varying excitation field is formed having one or more substantially rectangular components in the frequency domain. - View Dependent Claims (25, 26, 27, 28, 29)
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30. In an ion trap apparatus of the type having a ring electrode and end electrodes, a source of ions, and means for detecting ions to produce a signal indicative thereof, the improvement comprising:
excitation means connected to the end electrodes of the trap for producing an electric field in the trap, wherein the excitation means generates a sine wave signal at a selected frequency and a sinc function signal of a selected width and center time and multiplies the two signals to provide an excitation signal which is applied to electrodes of the ion trap, whereby the magnitude spectrum of the excitation signal in the frequency domain is a substantially rectangular function centered on the frequency of the sine wave signal and having a width determined by the width of the sinc function signal. - View Dependent Claims (31, 32, 33, 34, 35, 36, 37)
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38. A method of ejecting selected mass-to-charge ratio ions from an ion trap of the type having a ring electrode and end electrodes, comprising the steps of:
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(a) generating a sine wave signal at a selected frequency; (b) generating a sinc function signal having a selected width and center time; (c) multiplying the sine wave signal times the sinc function signal to provide an output excitation signal; and (d) applying a voltage to the end electrodes of the ion trap to create an electric field in the ion trap which has a time domain waveform which corresponds to the excitation signal waveform to eject ions having mass-to-charge ratios which generally correspond to the frequency of the sine wave signal in the excitation signal. - View Dependent Claims (42, 43)
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44. A method of obtaining mass spectra from a mass spectrometer having an ion trap, comprising the steps of:
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(a) generating a sine wave signal at a selected frequency and a sinc function signal having a selected width and center time and multiplying the two signals to provide an excitation signal, whereby the magnitude spectrum of the excitation signal in the frequency domain is a substantially rectangular function centered on the frequency of the sine wave signal and having a width determined by the width of the sinc function signal; (b) applying an electric field to the ion trap which has a time domain waveform which corresponds to the excitation signal at a power level to eject ions having mass to charge ratios near the frequency of the sine wave signal; and (c) thereafter applying a broad band excitation to the ion trap to acquire a mass spectrum containing peaks corresponding to the ions remaining in the trap.
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Specification