Time-of-flight mass spectrometer and a method of analysing ions in a time-of-flight mass spectrometer

Patent metadata

Field	Value
Publication number	US-9595432-B2
Application number	US-51823607-A
Country	US
Kind code	B2
Filing date	Dec 7, 2007
Priority date	Dec 11, 2006
Publication date	Mar 14, 2017
Grant date	Mar 14, 2017

Abstract

A time-of-flight mass spectrometer ( 1 ) comprises an ion source a segmented linear ion device ( 10 ) for receiving sample ions supplied by the ion source and a time-of-flight mass analyzer for analyzing ions ejected from the segmented device. A trapping voltage is applied to the segmented device to trap ions initially into a group of two or more adjacent segments and subsequently to trap them in a region of the segmented device shorter than the group of segments. The trapping voltage may also be effective to provide a uniform trapping field along the length of the device ( 10 ).

First claim

The invention claimed is:

1. A time-of-flight mass spectrometer comprising:
an ion source for supplying sample ions;
a segmented linear ion storage device for receiving the sample ions;
a voltage supply; and
a time-of-flight mass analyzer, and
wherein the segmented linear ion storage device comprises:
at least a pair of adjacent segments extending along a longitudinal axis of the ion storage device, and
an axially-extending region comprising a trapping volume of a group of two or more mutually adjacent segments of the device, and an extraction region that is shorter than the axially-extending region,

wherein the time-of-flight mass analyzer operates to perform mass analysis of ions ejected from the extraction region
wherein the voltage supply operates to supply to the device:
a trapping voltage including an RF trapping voltage, and
an extraction voltage, and
wherein the trapping voltage, with the assistance of cooling gas, is effective to trap the sample ions or ions derived from said sample ions in the trapping volume of the axially-extending region and to cause the trapped ions subsequently to become trapped in the extraction region to form an ion cloud,
wherein the RF trapping voltage creates a quadrupole trapping field that is substantially uniform along and between the pair of adjacent segments to enable ions to pass between the pair of adjacent segments without substantial loss of ions, and
wherein the extraction voltage is effective to cause ejection of the ion cloud from said extraction region in an extraction direction orthogonal to said longitudinal axis of the ion storage device,

wherein each segment comprises a respective plurality of electrode sections that each have an interior surface,
wherein, for each electrode section of a first segment of the pair of adjacent segments for which the interior surface is continuous, a respective distance from the longitudinal axis of the ion storage device to a nearest point to the longitudinal axis of the ion storage device along the interior surface of the electrode section is substantially equivalent to a same first distance,
wherein, for each electrode section of a second segment of the pair of adjacent segments for which the interior surface is continuous, a respective distance from the longitudinal axis of the ion storage device to a nearest point to the longitudinal axis of the ion storage device along the interior surface of the electrode section is substantially equivalent to a same second distance, and
wherein the first distance for the first segment is different than the second distance for the second segment.

2. A spectrometer as claimed in claim 1 wherein said extraction region comprises a trapping volume of a single segment of the device.

3. A spectrometer as claimed in claim 1 further comprising an ion cloud treatment mechanism for reducing the physical size of, and/or velocity spread of ions in said ion cloud in directions transverse to said longitudinal axis before said extraction voltage is applied.

4. A spectrometer as claimed in claim 3 wherein said ion cloud treatment mechanism is effective to encourage said ion cloud to form on said longitudinal axis before said extraction voltage is applied.

5. A spectrometer as claimed in claim 3 wherein said extraction region comprises a trapping volume of one or more extraction segments of the device and said ion cloud treatment mechanism is arranged to cause said voltage supply to increase a trapping voltage applied to said extraction region.

6. A spectrometer as claimed in claim 5 wherein said increase comprises a succession of stepped abrupt increases.

7. A spectrometer as claimed in claim 3 wherein said extraction region comprises a trapping volume of one or more extraction segments of the device and said ion cloud treatment mechanism is arranged to cause said voltage supply to terminate a trapping voltage applied to said one or more extraction segment and to impose a delay between termination of the trapping voltage and application of the extraction voltage.

8. A spectrometer as claimed in claim 7 wherein said voltage supply applies an intermediate voltage to said one or more extraction segment during said delay.

9. A spectrometer as claimed in claim 3 wherein said trapping voltage is also effective to compress said ion cloud axially within said extraction region.

10. A spectrometer as claimed in claim 2 wherein the single segment of said extraction region is an extraction segment of the device, and wherein said extraction segment includes a first respective electrode section which, when supplied with a first level of said trapping voltage enables ions to form a substantially one-dimensional axially extending ion cloud within the extraction region and a second respective electrode section which, when supplied with a second level of said trapping voltage is effective to transform said substantially one-dimensional axially extending cloud to form a substantially two-dimensional ion cloud in a central plane orthogonal to said extraction direction.

11. A spectrometer as claimed in claim 10 wherein said substantially two-dimensional ion cloud is a toroidally shaped ion cloud.

12. A spectrometer as claimed in claim 10 comprising an ion cloud treatment mechanism for reducing the physical size of, and/or velocity spread of ions in the ion cloud in directions transverse to said longitudinal axis before and/or after said second level of said trapping voltage is applied.

13. A spectrometer as claimed in claim 1 wherein said device has an entrance end and an exit end, an ion detection mechanism located at said exit end, and said voltage supply is arranged to allow sample ions to pass through said device from said entrance end to said exit end for detection by said ion detection mechanism and subsequently to trap ions received within the device from said ion source and prevent further ions from entering the device after a time interval determined by an ion current detected by said ion detection mechanism.

14. A spectrometer as claimed in claim 1 wherein said trapping voltage is effective to trap sample ions in an ion storage region of the device located between an entrance end of the device and the axially-extending region of the device and subsequently to cause ions to pass from said ion storage region into another region of the device whilst simultaneously trapping further sample ions in the ion storage region.

15. A spectrometer as claimed in claim 14 wherein said ion storage region comprises a trapping volume of a single segment of the device.

16. A spectrometer as claimed in claim 14 wherein said another region is said axially extending region.

17. A spectrometer as claimed in claim 14 wherein voltage supplied to said device by said voltage supply causes ions to undergo fragmentation and/or isolation in a region or regions outside said ion storage region whilst simultaneously trapping further sample ions in said ion storage region.

18. A spectrometer as claimed in claim 1 wherein said trapping voltage is effective to trap ions in a fragmentation region of the device, and said voltage supply is arranged to supply fragmentation voltage to the device to cause fragmentation of ions trapped in the fragmentation region.

19. A spectrometer as claimed in claim 18 wherein said fragmentation voltage comprises dipole excitation voltage effective to cause fragmentation of ions in a selected range of mass-to-charge ratio.

20. A spectrometer as claimed in claim 19 wherein said dipole excitation

Assignees

• Giles Roger
• Sudakov Michael
• Wollnik Hermann
• Shimadzu Corp

Inventors

• Giles Roger
• Sudakov Michael
• Wollnik Hermann

Classifications

• H01J49/4295

  Storage methods · CPC title

• H01J49/403 Primary

  characterised by the acceleration optics and/or the extraction fields · CPC title