Linear Ion Trap Analyzer

• US 20120248307A1
• Filed: 04/04/2011
• Published: 10/04/2012
• Est. Priority Date: 04/04/2011
• Status: Active Grant

• Current Assignee: Shimadzu Corporation
• Original Assignee: Shimadzu Corporation
• Inventors: Ding, Li, Lin, Tao, Jiang, Gongyu, Mu, Hui
• Granted Patent: US 8,759,759 B2
• Time in Patent Office: Days
• US Class Current: 250/293
• CPC Class Codes: H01J 49/423 with radial ejection

Abstract

The present invention relates generally to the field of ion storage and analysis, in particular to a linear ion trap mass analyzer comprised by multiple columnar electrodes. High frequency voltages are applied on at least one of the columnar electrodes to form ion confining space, which mainly consists of two-dimensional quadrupole electric radial trapping field, and there is at least one through slot for ion ejection in at least one direction perpendicular to the axis of the ion trap, wherein an AC electric field superposition is applied to invoke dipole excitation. Opposite to the through slot, there is an elongated electrode for field adjusting between two columnar electrodes or inside the slit of one of the columnar electrodes mentioned above. The potential on the elongated electrode for field adjusting is set as the sum of a portion of the high frequency voltage which applied on one adjacent columnar electrode and a DC offset, which can be adjusted freely. Through adjusting the portion of the high frequency potential and DC potential on this electrode, one or more objectives, including field optimization inside the ion trap as well as ion motion characteristics of resonant ejection, can be realized.

Claims

1. A linear ion trap analyzer, comprising, a ion trapping volume surrounded by multiple columnar electrodes, whereas, the generatrix of said columnar electrodes are parallel to the central axis of the trapping volume, at least a part of said columnar electrodes is applied with high frequency voltage to form in said trapping volume a trapping electric field which is dominated by two-dimensional quadrupole field;

at least one through slot for ion ejection orientated in one direction perpendicular to the said axis, wherein an AC electric field superposition is applied to invoke dipole excitation in said one direction;

a field adjusting electrode opposite to said through slot placed between two columnar electrodes or inside the slot of one of the columnar electrodes, wherein the potential of said field adjusting electrode is set as the sum of a portion of the high frequency voltage applied to one adjacent columnar electrode and an adjustable DC voltage offset.

2. The linear ion trap analyzer according to claim 1, further includes an electric circuit for applying voltages to the said field adjusting electrode comprising a capacitor for coupling the high frequency voltage to the said field adjusting electrode from the said adjacent columnar electrode, and a resistor and/or an inductor for applying a DC voltage superposition on the said high frequency voltage, and the DC voltage is provided by a controllable DC voltage source.

3. The linear ion trap analyzer according to claim 1, further includes an electric circuit for applying voltages to the said field adjusting electrode comprising a capacitor for coupling the high frequency voltage to the said field adjusting electrode from the said adjacent columnar electrode, and a diode for applying a DC voltage superposition on said high frequency voltage, wherein the DC voltage is controlled by a DC voltage power supply and the DC amplitude of the said power supply substantially equals to the sum of the required DC voltage offset of field adjusting electrode and the positive or negative peak value of the said high frequency voltage.

4. The linear ion trap analyzer according to claim 1, wherein at least part of the surface of the said columnar electrodes is hyperbolic columnar surface.

5. The linear ion trap analyzer according to claim 1, wherein at least part of the surface of the said columnar electrodes is planar columnar surface.

6. The linear ion trap analyzer according to claim 1, wherein at least part of the surface of the said columnar electrodes is step shaped columnar surface.

7. The linear ion trap analyzer according to claim 1, wherein at least part of the columnar surface of the said columnar electrodes has planar patterns of printed circuits on the surface.

8. The linear ion trap analyzer according to claim 1, wherein the said field adjusting electrodes comprise one or multiple sections of segmented electrodes.

9. The linear ion trap analyzer according to claim 1, wherein the said high frequency voltages are generated by digital switches and in rectangular waveforms.

10. The linear ion trap analyzer according to claim 1, wherein the strength or the frequency of the trapping electric field is scanned while the said AC electric field superposition is applied to invoke dipole excitation in the direction perpendicular to the said axis and to invoke the ions trapped inside the linear ion trap to eject resonantly according to their mass-to-charge ratios;

and also includes controlling means to alter the DC voltage applied on the said field adjusting electrode when the said scan is reversed or the scan speed is changed.

11. The linear ion trap analyzer according to claim 1, wherein the said value of DC voltage applied on the said field adjusting electrode is adjusted to improve the ejection efficiency through the outlet slot opposite to the field adjusting electrode during the scan where ions eject out resonantly according to their mass-to-charge ratios.

12. The linear ion trap analyzer according to claim 1, wherein the value of DC voltage applied on the said field adjusting electrode is set to generate a DC high order field during the said AC electric field is applied to invoke dipole excitation of at least one ion, wherein the DC high order field alters the secular frequency of the said at least one ion from the frequency of the said AC electric field and break its resonance when the amplitude of the ion motion is close to the field radius of the linear ion trap, so that the ion avoids being further excited.