US4766312A
Expired / Lapsed
US
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Methods and apparatus for detecting negative ions from a mass spectrometer
Assignee: Applied Biosystems LLC
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Filing: 1987-05-15
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Granted: 1988-08-23
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Expires: 2007-05-15
Abstract
Abstract Improved methods and apparatus are disclosed for detecting negative ions and, more particularly, for detecting negative ions produced from a quadrupole mass spectrometer. By modulating the ion beam either at the ion source or within the ion focusing system, the output current from the electron multiplier detector is a pulsating current which is then capacitively or inductively coupled from a high direct current potential to ground level. Electronics operating at ground level are employed to correct the current signal distortion due to the capacitive or inductive coupling of the detector output current. The present invention enables substantially increased detector sensitivity to negative ions compared to prior art equipment, and does not require expensive and complex preamplifier circuitry. The techniques of the present invention allow both positive and negative ions to be detected utilizing the same basic equipment, thereby increasing equipment versatility and reducing costs.
Inventors
- 👤 Gordon J. Fergusson
- 👤 Marvin L. Vestal
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 23:50
CPC Classifications
H; H01; H01J; H01J49/00; H01J49/02; H01J49/025
Claims Analysis
Total Claims: 25
Claim 1
Independent Claim
269 words
An improved mass spectrometry system for analyzing the composition of a sample, including an ion source and focusing means for generating an ion beam having ions representative of the sample, a mass analyzer for scanning selected ions from the beam either at a specific atomic mass unit or over a range of atomic mass units, and an ion detector having an electron multiplier with an anode and cathode for receiving ions from the beam discharged from the mass analyzer and for providing a detector output signal indicative of the intensity of ions at a specific atomic mass unit and representative of the composition of the sample, the system further comprising: power supply means for charging the cathode at a high negative potential to attract positive ions or at a high positive potential to attract negative ions while maintaining the anode at a positive potential relative to the cathode; means for modulating the ion beam to the mass analyzer for producing a modulated ion beam to the detector and a modulated high-voltage output signal from the detector; circuitry means for capacitively or inductively coupling the modulated high-voltage output signal to ground and providing a coupled output signal functionally related to the modulated high-voltage output signal; sensing means for measuring distortion of the coupled output signal introduced by the capacitive or inductive coupling of the modulated high-voltage output signal to ground; and signal modification means for correcting the coupled output signal in response to the measured coupled output signal distortion to provide a modified coupled output signal representative of the modulated high-voltage output signal and thus the composition of the sample.
Claim 2
Dependent Claim
269 words
An improved mass spectrometry system for analyzing the composition of a sample, including an ion source and focusing means for generating an ion beam having ions representative of the sample, a mass analyzer for scanning selected ions from the beam either at a specific atomic mass unit or over a range of atomic mass units, and an ion detector having an electron multiplier with an anode and cathode for receiving ions from the beam discharged from the mass analyzer and for providing a detector output signal indicative of the intensity of ions at a specific atomic mass unit and representative of the composition of the sample, the system further comprising: power supply means for charging the cathode at a high negative potential to attract positive ions or at a high positive potential to attract negative ions while maintaining the anode at a positive potential relative to the cathode; means for modulating the ion beam to the mass analyzer for producing a modulated ion beam to the detector and a modulated high-voltage output signal from the detector; circuitry means for capacitively or inductively coupling the modulated high-voltage output signal to ground and providing a coupled output signal functionally related to the modulated high-voltage output signal; sensing means for measuring distortion of the coupled output signal introduced by the capacitive or inductive coupling of the modulated high-voltage output signal to ground; and signal modification means for correcting the coupled output signal in response to the measured coupled output signal distortion to provide a modified coupled output signal representative of the modulated high-voltage output signal and thus the composition of the sample.
Claim 3
Dependent Claim
46 words
An improved system as defined in claim 1, wherein the cathode of the electron multiplier is charged in the range of from +1kV to +4kV while the anode of the electron multiplier is maintained in the range of from +1kV to +3kV relative to the cathode.
Claim 4
Dependent Claim
41 words
An improved system as defined in claim 1, wherein the cathode of the electron multiplier is charged in the range of from-1kV to -5kV while the anode is maintained in the range of from +1kV to +3kV relative to the cathode.
Claim 5
Dependent Claim
27 words
An improved system as defined in claim 1, wherein the sensing means generates a correction signal as a function of a peak of the coupled output signal.
Claim 6
Dependent Claim
29 words
An improved system as defined in claim 4, wherein a decay time constant of the correction signal is less than a decay time constant of the coupled output signal.
Claim 7
Dependent Claim
30 words
An improved system as defined in claim 5, wherein the decay time constant of the correction signal is substantially equal to the decay time constant of the coupled output signal.
Claim 8
Dependent Claim
80 words
An improved system as defined in claim 1, wherein the circuitry means further comprises: a current to voltage converter for converting a current value of the coupled output signal to a voltage output indicative of the current value; and offsetting means for maintaining a constant voltage output in response to preselected low-level variations in the input current to the converter while the voltage output remains indicative of current values for coupled output signals representative of the composition of the sample.
Claim 9
Dependent Claim
136 words
An improved negative ion detector means for a scanning mass spectrometry system for analyzing the composition of a sample, the system including an ion source for producing an ion beam having ions representative of the sample, a mass analyzer for scanning selected ions from the beam over a range of atomic mass units, and power supply means for maintaining a cathode of an electron multiplier of the detector at a high positive potential and an anode of the electron multiplier at a higher positive potential for attracting negative ions, the detector means being charged by the power supply means for receiving negative ions discharged from the mass analyzer and providing a high-voltage output signal over the range of atomic mass units for analyzing the composition of the sample, the improved negative ion detector means further comprising
Claim 10
Dependent Claim
136 words
An improved negative ion detector means for a scanning mass spectrometry system for analyzing the composition of a sample, the system including an ion source for producing an ion beam having ions representative of the sample, a mass analyzer for scanning selected ions from the beam over a range of atomic mass units, and power supply means for maintaining a cathode of an electron multiplier of the detector at a high positive potential and an anode of the electron multiplier at a higher positive potential for attracting negative ions, the detector means being charged by the power supply means for receiving negative ions discharged from the mass analyzer and providing a high-voltage output signal over the range of atomic mass units for analyzing the composition of the sample, the improved negative ion detector means further comprising
Claim 11
Dependent Claim
78 words
circuitry means for capacitively or inductively coupling the high-voltage output signal to ground potential and providing a coupled output signal functionally related to the high-voltage output signal; sensing means for measuring distortion of the coupled output signal introduced by the capacitive or inductive coupling; and correcting means for altering the coupled output signal in response to the measured coupled output signal distor- tion to provide a modified essentially ground-voltage coupled output signal representative of the high-voltage output signal.
Claim 12
Dependent Claim
78 words
circuitry means for capacitively or inductively coupling the high-voltage output signal to ground potential and providing a coupled output signal functionally related to the high-voltage output signal; sensing means for measuring distortion of the coupled output signal introduced by the capacitive or inductive coupling; and correcting means for altering the coupled output signal in response to the measured coupled output signal distor- tion to provide a modified essentially ground-voltage coupled output signal representative of the high-voltage output signal.
Claim 13
Dependent Claim
24 words
An improved negative ion detector means as defined in claim 8, wherein the circuitry means capacitively couples the high-voltage output signal to ground potential.
Claim 14
Dependent Claim
50 words
An improved negative ion detector means as defined in claim 8, wherein the cathode of the electron multiplier is charged by the power supply means to the range of from +1kV to +4kV while the anode of the electron multiplier is maintained in the range of from +2kV to +5kV.
Claim 15
Dependent Claim
30 words
An improved negative ion detector means as defined in claim 8, wherein the sensing means generates a correction signal as a function of a peak of the coupled output signal.
Claim 16
Dependent Claim
37 words
An improved negative ion detector means as defined in claim 11, wherein a decay time constant of the correction signal is less than and substantially equal to a decay time constant of the coupled detector output signal.
Claim 17
Dependent Claim
246 words
In a mass spectrometry system for analyzing the composition of a sample, the system including an ion source for producing an ion beam having ions representative of the sample, a mass analyzer for scanning selected ions from the beam either at specific atomic mass unit or over a range of atomic mass units, and an ion detector having an electron multiplier with an anode and cathode for receiving ions from the beam discharged from the mass analyzer, an improved method of obtaining an output signal indicative of the intensity, of ions at a specific atomic mass unit and representative of the composition of the sample, the method comprising: charging the cathode at a high negative potential to attract positive ions or at a high positive potential to attract negative ions while maintaining the anode at a positive potential relative to the cathode; modulating the ion beam to the mass analyzer to produce a modulated ion beam to the detector and a modulated high-voltage output signal from the detector; capacitively or inductively coupling the modulated high-voltage output signal to ground and providing a coupled output signal functionally related to the modulated high-voltage output signal; measuring distortion of the coupled output signal introduced by the capacitive or inductive coupling of the modulated high-voltage output signal to ground; and correcting the coupled output signal in response to the measured coupled output signal distortion to provide an essentially ground-voltage modified coupled output signal representative of the modulated high-voltage output signal.
Claim 18
Dependent Claim
246 words
In a mass spectrometry system for analyzing the composition of a sample, the system including an ion source for producing an ion beam having ions representative of the sample, a mass analyzer for scanning selected ions from the beam either at specific atomic mass unit or over a range of atomic mass units, and an ion detector having an electron multiplier with an anode and cathode for receiving ions from the beam discharged from the mass analyzer, an improved method of obtaining an output signal indicative of the intensity, of ions at a specific atomic mass unit and representative of the composition of the sample, the method comprising: charging the cathode at a high negative potential to attract positive ions or at a high positive potential to attract negative ions while maintaining the anode at a positive potential relative to the cathode; modulating the ion beam to the mass analyzer to produce a modulated ion beam to the detector and a modulated high-voltage output signal from the detector; capacitively or inductively coupling the modulated high-voltage output signal to ground and providing a coupled output signal functionally related to the modulated high-voltage output signal; measuring distortion of the coupled output signal introduced by the capacitive or inductive coupling of the modulated high-voltage output signal to ground; and correcting the coupled output signal in response to the measured coupled output signal distortion to provide an essentially ground-voltage modified coupled output signal representative of the modulated high-voltage output signal.
Claim 19
Dependent Claim
42 words
A method as defined in claim 13, wherein the cathode of the electron multiplier is charged in the range of from +1kV to +4 kV while the anode of the electron multiplier is maintained in the range of from +2kV to +5kV.
Claim 20
Dependent Claim
37 words
A method as defined in claim 13, wherein the anode of the electron multiplier is maintained in the range of from -1kV to -4kV while the cathode is charged in the range of from -2kV to -5kV.
Claim 21
Dependent Claim
34 words
A method as defined in claim 13, wherein the step of measuring distortion of the coupled output signal comprises generating a correction signal as a function of a peak of the coupled output signal.
Claim 22
Dependent Claim
30 words
A method as defined in claim 16, wherein a selected decay time constant of the correction signal is less than a selected decay time constant of the coupled output signal.
Claim 23
Dependent Claim
31 words
A method as defined in claim 17, wherein the selected decay time constant of the correction signal is substantially equal to the selected decay time constant of the coupled output signal.
Claim 24
Dependent Claim
18 words
A method as defined in claim 13, wherein the modulated high-voltage output signal is capacitively coupled to ground.
Claim 25
Dependent Claim
63 words
A method as defined in claim 13, further comprising: converting a current value of the coupled output signal to a voltage output indicative of the current value; and maintaining a constant voltage output in response to preselected low-level variations in the current input while the voltage output remains indicative of current values for coupled output signals representative of the composition of the sample.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1991-08-23 | 1992-02-22 | 1992-08-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-08-23 | 1996-02-22 | 1996-08-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-08-23 | 2000-02-22 | 2000-08-23 | $7700.00 | Window Closed / Lapsed |