Mass analyzing method using an ion trap type mass spectrometer
View Patent ↗The present invention provides a method of discriminating singly-charged ions from multiply-charged ions by the use of an ion trap type mass spectrometer which is an inexpensive mass spectrometer. This is achieved by a mass-analyzing method using an ion trap type mass spectrometer equipped with a ring electrode and one pair of end cap electrodes to temporarily trap ions in a three-dimensional quadrupole field to mass-analyze a sample. The method includes a first step of applying a main high frequency voltage to the ring electrode to form a three-dimensional quadrupole field, a second step of generating ions in the mass analyzing unit or injecting ions from the outside and trapping ions of a predetermined mass-to-charge ratio range in the mass analyzing unit, a third step of applying a supplementary AC voltage having a plurality of frequency components between the end cap electrodes and scanning the frequency components of the supplementary AC voltage, and a fourth step of scanning the main high frequency voltage and ejecting ions from the mass analyzing unit, and detection thereof. With this, chemical noises can be reduced dramatically.
1. A mass analyzing method using an ion trap mass spectrometer which is equipped with a ring electrode and one pair of end electrodes and temporarily traps ions in a three-dimensional quadrupole field to mass-analyze a sample, comprising:
a first step of applying a main high frequency voltage to said ring electrode to form a three-dimensional quadrupole field,
a second step of generating ions in a mass-analyzing unit or injecting ions from the outside and trapping ions of a predetermined mass-to-charge ratio range in said mass analyzing unit,
a third step of applying a supplementary AC voltage having a plurality of frequency components between said end cap electrodes and scanning said main high frequency voltage, said supplementary AC voltage having a first frequency component with a voltage value (V 1 ) at least high enough to eject ions in resonance and a second frequency component with a voltage value (V 2 ) high enough to excite ions in resonance but not high enough to eject ions in resonance,
a fourth step of scanning said main high frequency voltage and ejecting ions from said mass analyzing unit and detecting them.
2. A mass analyzing method in accordance with claim 1 , wherein said supplementary AC voltage has a predetermined frequency band (ω 1 to ω 2 ).
3. A mass analyzing method in accordance with claim 1 , wherein the low frequency component of said supplementary AC voltage has said voltage value V 1 .
4. A mass analyzing method in accordance with claim 3 , wherein the frequency and voltage values of said supplementary AC voltage in said third step are fixed and said main high frequency voltage is swept from high voltage to low voltage.
5. A mass analyzing method in accordance with claim 3 , wherein a step is provided between said second step and said third step to apply a wide-band noise signal to said end cap electrodes to exclude ions of a high-mass region.
6. A mass analyzing method in accordance with claim 1 , wherein the higher frequency component of said supplementary AC voltage has said voltage value V 1 .
7. A mass analyzing method in accordance with claim 1 , wherein the frequency and voltage values of said supplementary AC voltage in said third step are fixed and said main high frequency voltage is swept from low voltage to high voltage.
8. A mass analyzing method in accordance with claim 6 , wherein a step is provided between said second step and said third step to apply a wide-band noise signal to said end cap electrodes to exclude ions of a low-mass region.
9. A mass analyzing method in accordance with claim 1 , wherein said second frequency component is a wide-band noise component.
10. A mass analyzing method in accordance with claim 9 , wherein said wide-band noise component is continuous.
11. A mass analyzing method in accordance with claim 9 , wherein said wide-band noise component is discrete.
12. A mass analyzing method in accordance with claim 1 , wherein said first frequency component is a signal frequency component.
13. A mass analyzing method in accordance with claim 1 , wherein said first frequency is a plural frequency component.