Quantitative measurements of elemental and molecular species using high mass resolution mass spectrometry

Patent metadata

Field	Value
Publication number	US-10403487-B2
Application number	US-201615235519-A
Country	US
Kind code	B2
Filing date	Aug 12, 2016
Priority date	Aug 14, 2015
Publication date	Sep 3, 2019
Grant date	Sep 3, 2019

Abstract

A method for generating a mass spectrum of sample ions using a multi-collector mass spectrometer is disclosed. The mass spectrometer includes a spatially dispersive mass analyser to direct the sample ions into a detector chamber. The method includes generating sample ions of a first ion species A, a second ion species B, and a third ion species C, wherein the ions of species A have a different nominal mass to the ions of species B and C, and further wherein the ions of species B have the same nominal mass as the ions of species C. The sample ions of the species A, B and C are directed to travel through the mass analyser and towards detectors in the detector chamber, the sample ions being deflected during their travel. The ions of species B and C are scanned across a master aperture defined in a master mask of a master detector, while the ions of species A pass through a lead aperture defined in a lead mask of a lead detector. A lead signal is generated representing the ion intensity received at the lead detector from the ions of species A, and generating a master signal representing the ion intensity received at the master detector whilst the ions of species B and C are scanned across the master aperture. During scanning, ions of the species A are detected by the lead detector while ions of the species B but not C, then both species B and species C, and then species C but not B are detected by the master detector.

First claim

The invention claimed is:

1. A method for generating a mass spectrum of sample ions using a multi-collector mass spectrometer, the mass spectrometer including a spatially dispersive mass analyzer to direct the sample ions into a detector chamber, the method comprising:
(a) generating sample ions of a first ion species A having a mass to charge ratio (m/z) A , a second ion species B having a mass to charge ratio (m/z) B , and a third ion species C having a mass to charge ratio (m/z) C , wherein the ions of species A have a different nominal mass to the ions of species B and C, and further wherein the ions of species B have the same nominal mass as the ions of species C;
(b) directing the sample ions of the species A, B and C to travel through the mass analyzer and towards detectors in the detector chamber, the sample ions being deflected during their travel;
(c) scanning the ions of species B and C across a master aperture defined in a master mask of a master detector, while the ions of species A pass through a lead aperture defined in a lead mask of a lead detector; and
(d) generating a lead signal representing the ion intensity received at the lead detector from the ions of species A, and generating a master signal representing the ion intensity received at the master detector while the ions of species B and C are scanned across the master aperture;
wherein, during scanning, ions of the species A are detected by the lead detector while ions of the species B but not C, then both species B and species C, and then species C but not B are detected by the master detector.

2. The method according to claim 1 , further comprising
(e) normalizing the master signal from the ions B and the ions C using the lead signal to determine a normalized mass spectrum of the ions B and the ions C.

3. The method according to claim 1 , wherein one or both of the lead detector and master detector is an ion counting detector.

4. The method according to claim 1 , wherein one or both of the lead detector and master detector is a Faraday detector.

5. The method according to claim 1 , wherein while the ions of species B and C are scanned across the master aperture, the method further comprises scanning the ions of species A across at least a portion of the lead aperture of the lead mask of the lead detector.

6. The method according to claim 1 , wherein the lead aperture is wider than the master aperture.

7. The method according to claim 1 , wherein the lead aperture and master aperture have same width.

8. The method according to claim 1 , wherein a lead pre-aperture deflection unit located downstream of the mass analyzer and in front of the lead aperture deflects the ion species A such that the ion species A fully passes through the lead aperture while the ions of species B and C are scanned across the master aperture.

9. The method according to claim 1 , wherein for all times when at least one of the ion species B and C is being collected by the master detector, ions of the species A are passing through the lead aperture and are collected by the lead detector.

10. The method according to claim 1 , wherein scanning the ions of species B and C comprises adjusting the deflection of ions of species B and C during their travel through the mass analyzer and towards detectors in the detector chamber.

11. The method according to claim 1 , wherein the ion species B and C are scanned across the master aperture by changing a deflection caused by a master pre-aperture deflection unit located downstream of the mass analyzer and in front of the master aperture.

12. The method according to claim 11 , wherein the deflection of ion species A is not changed while the deflection of ion species B and C is changed using the master pre-aperture deflection unit.

13. The method according to claim 1 , wherein the ion species B and Care scanned across the master aperture by ramping a magnetic field at the mass analyzer.

14. The method according to claim 1 , wherein the ion species B and Care scanned across the master aperture by adjusting an electric field at an electrostatic sector of the mass analyzer.

15. The method according to claim 1 , wherein the ion species B and C are scanned across the master aperture by changing a deflection by adjusting an energy of the sample ions.

16. The method according to claim 1 , wherein the ion species B and C are scanned across the master aperture by moving the master aperture.

17. The method according to claim 1 , wherein the ions of species A comprise a first species of atomic isotope, the ions of species B comprise a second species of atomic isotope and the ions of species C comprise a species of molecular isotope.

18. The method according to claim 1 , wherein the ions of species A comprise a first species of molecular isotope, the ions of species B comprise a second species of molecular isotope and the ions of species C comprise a third species of molecular isotope.

19. The method according to claim 1 , wherein the method further comprises positioning the lead detector within the detector chamber to receive the ions of species A.

20. The method according to claim 1 , wherein the method further comprises positioning the master detector within the detector chamber to receive the ions of species B and the ions of species C.

21. The method according to claim 1 , wherein the mass spectrometer comprises a plurality of detectors in the detector chamber, each detector comprising a mask defining an aperture, the method further comprising:
selecting the lead detector and/or the master detector from the plurality of detectors to select a width of the lead and/or master apertures respectively.

22. The method according to claim 2 , wherein determining a normalized mass spectrum of the ions B and the ions C comprises dividing the master signal at a given point in time by the lead signal acquired at the same point in time.

23. The method according to claim 2 , wherein the normalized mass spectrum of the ions of species B and ions of species C is a first normalized mass spectrum, the method further comprising:
generating a second normalized mass spectrum; and
determining an average normalized mass spectrum from an average of the first and second normalized mass spectrum.

24. The method according to claim 1 , further comprising changing the rate of adjusting the deflection so as to scan the ions of species A and/or B and C at a plurality of different scan rates as they are scanned across the respective lead and/or master apertures.

25. Apparatus for generating a mass spectrum of sample ions using a multi-collector mass spectrometer containing a spatially dispersive mass analyzer, the sample ions being directed to travel through the mass analyzer and towards detectors in a detector chamber wherein the sample ions are deflected during their travel, the mass spectrometer including a lead detector arranged in the detector chamber to receive sample ions of a first ion species A having a mass to charge ratio (m/z) A , and a master detector arranged in the detector chamber to receive sample ions of a second ion species B having a mass to charge ratio (m/z) B and a third ion species C having a mass to charge ratio (m/z) C , and wherein the ions of species A have a different nominal mass to the ions of species B and C, and further wherein the ions of species B have the same nominal mass as the ions of species C, the apparatus comprising:
a control module

Assignees

• Thermo Fisher Scient Bremen Gmbh

Inventors

• Schwieters Johannes
• Deerberg Michael
• Krummen Michael

Classifications

• H01J49/025 Primary

  Detectors specially adapted to particle spectrometers (data acquisition H01J49/0036; detectors per se G01T, e.g. G01T1/28, G01T1/29) · CPC title

• H01J49/0027

  Methods for using particle spectrometers · CPC title

• H01J49/32 Primary

  using double focusing · CPC title

• H01J49/26 Primary

  Mass spectrometers or separator tubes · CPC title

• G01N27/62

  by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode · CPC title