Quadrupole mass spectrometer

• US 5,227,629 A
• Filed: 11/29/1991
• Issued: 07/13/1993
• Est. Priority Date: 11/30/1990
• Status: Expired due to Term

• Current Assignee: Shimadzu Corporation
• Original Assignee: Shimadzu Corporation
• Inventors: Miseki, Kozo
• Primary Examiner(s): Dzierzynski, Paul M.
• Assistant Examiner(s): NGUYEN, KIET TUAN
• Application Number:
  US07/800,069
• Time in Patent Office: 592 Days
• Field of Search: 250/292, 250/290, 250/293, 250/281, 250/282
• US Class Current: 250/292
• CPC Class Codes: H01J 49/421 Mass filters, i.e. deviating unwanted ions without trapping

Abstract

A small AC voltage V_a ·cosω_a t (perturbation AC voltage) is applied to the electrodes of a quadrupole mass spectrometer besides the normal DC and AC voltages U and V·cosωt (mass scanning voltages). The perturbation AC voltage generates unstable bands UB1, UB2 in a triangular stable region SR and cut off the skirts of the peak profile of every mass, which enhances the resolution of masses in the mass spectroscopy and improves the reliability of the measurement results.

Claims

1. A quadrupole mass spectrometer comprising:

means for discriminating ions by mass;

said means for discriminating ions by mass comprising;

(a) a first pair of rod electrodes both placed parallel to a center axis in a first plane;

(b) a second pair of rod electrodes both placed parallel to the center axis in a second plane perpendicularly intersecting the first plane at the center axis;

(c) a DC source for applying a DC voltage U between the first pair of electrodes and the second pair of electrodes;

(d) a first AC source for applying a first AC voltage having an amplitude V and a frequency ω

between the first pair of electrodes and the second pair of electrodes; and

(e) a second AC source for applying a second AC voltage between the first pair of electrodes and the second pair of electrodes, the amplitude V_a of the second AC voltage being smaller than the amplitude V of the first AC voltage and the frequency ω

_a of the second AC voltage being different from the frequency ω

of the first AC voltage.

2. A quadrupole mass spectrometer, as claimed in claim 1, where the second AC voltage is applied when the quadrupole mass spectrometer is scanning through masses that are heavier than a predetermined threshold mass.

3. A quadrupole mass spectrometer, as claimed in claim 2, where the amplitude V_a of the second AC voltage increases as the mass increases while the quadrupole mass spectrometer is scanning.

4. A quadrupole mass spectrometer, as claimed in claim 3, where the amplitude V_a of the second AC voltage is set proportional to the difference between the DC voltage U and a reference value U_t which is changed directly proportional to the mass m, as

5. A quadrupole mass spectrometer, as claimed in claim 4, where the second AC voltage is applied to either one of the first pair of electrodes or the second pair of electrodes.

6. A quadrupole mass spectrometer, as claimed in claim 2, where the second AC voltage is applied to either one of the first pair of electrodes or the second pair of electrodes.

7. A quadrupole mass spectrometer, as claimed in claim 3, where the second AC voltage is applied to either one of the first pair of electrodes or the second pair of electrodes.

8. A quadrupole mass spectrometer, as claimed in claim 1, where the second AC voltage is applied to either one of the first pair of electrodes or the second pair of electrodes.