Claims
- 1. The method of mass analyzing a sample which comprises the steps of:
- defining a three-dimensional electrical quadrupole storage field in which sample ions over the entire mass range of interest can be simultaneously trapped;
- introducing or creating sample ions into the quadrupole field whereby ions within the mass range of interest are simultaneously trapped and perform ion-mass specific secular movements;
- superimposing an exciting RF field with a frequency different from that of the storage RF field;
- changing the superimposed fields so that simultaneously and stably trapped ions of consecutive masses encounter a resonance of their secular movements with the exciting RF field, take up energy, increase thereby the secular movement amplitudes, and leave the trapping field;
- detecting the ions of sequential masses as they leave the trapping field; and
- providing an output signal indicative of the ion mass.
- 2. The method of claim 1 in which the storage field is generated by a QUISTOR of the type having a ring electrode and spaced end electrodes where the storage field is defined by U, V.sub.stor, and f.sub.stor, and the exciting field is defined by V.sub.exc and f.sub.exc, and in which the superimposed fields are changed by one or more of U, V.sub.stor, f.sub.stor, or f.sub.exc, where:
- U=amplitude of DC voltage between the ring electrode and the end electrodes
- V.sub.stor =magnitude of storage RF voltage between ring electrode and end electrodes
- f.sub.stor =frequency of RF voltage
- V.sub.exc =magnitude of exciting RF voltage between the two end electrodes
- f.sub.exc =frequency of exciting RF voltage.
- 3. The method of claim 2 in which f.sub.exc is set constant, and essentially only V.sub.stor is changed.
- 4. The method of claim 3 in which the constant frequency f.sub.exc of the exciting field matches a sum or coupling resonance frequency arising from geometrical deviations of the storing field from the angle, 1:1.414 of the asymptotes, or from electrical deviations of the RF voltage from ideal sine waves.
- 5. The method of claim 4 in which said sum or coupling resonances of the secular movements of the ions are generated by geometrical deviations of the storing field introduced by deviations of the shape of the ring and end electrodes from the ideal hyperbolic form with angle 1:1.414 of the asymptotes.
- 6. The method of claim 5 in which the radii of the curved end electrodes and of the curved ring electrode, both defined in the points nearest to the field center, in order to generate the resonances of the secular movements obey the condition ##EQU3## R.sub.e =radius of the end electrodes in the points nearest to the field center
- R.sub.r =radius of the ring electrode in the points nearest to the field center
- r.sub.o =smallest distance of the ring electrode from the field center
- z.sub.O =smallest distance of the end electrodes from the field center.
- 7. The method of claim 5 in which the radii of the curved end electrodes and of the curved ring electrode, both defined in the points nearest to the field center, in order to generate the resonances of the secular movements obey the condition
- 4.010<Q<25.0.
- 8. A method as in claim 4 in which the shape of the QUISTOR electrodes are chosen so that the coupling resonance frequency of the secular ion movements coincides with a low fraction 1/n (n=small integer number greater then 2) of the storage frequency, and in which the excitation voltage with frequency f.sub.exc =f.sub.stor /n is coupled in frequency and phase to the storage voltage with frequency f.sub.stor.
- 9. A method as in claim 8 in which n=3.
- 10. A method as in claim 1 in which the scanning speed for the parameters of the superimposed fields is chosen such that the shift of the secular frequency with increasing amplitude, caused by an anharmonic storage field, is at least partially compensated by an inverse shift of the secular frequency caused by the parameter scanning itself.
GOVERNMENT INTEREST
The U.S. Government has rights in this invention pursuant to contract number DAAA-15-87-C-0008 awarded by the Department of the Army.
US Referenced Citations (2)
Number |
Name |
Date |
Kind |
4540884 |
Stafford et al. |
Sep 1985 |
|
4749860 |
Kelley et al. |
Jun 1988 |
|