Ion detecting apparatus and methods

• US 20030141446A1
• Filed: 01/24/2003
• Published: 07/31/2003
• Est. Priority Date: 01/25/2002
• Status: Active Grant

• Current Assignee: Interlink Electronics Incorporated
• Original Assignee: William C. Blanchard
• Inventors: Blanchard, William C.
• Granted Patent: US 6,924,479 B2
• Time in Patent Office: Days
• US Class Current: 250/287
• CPC Class Codes: H01J 49/025 Detectors specially adapted to particle spectrometers data acquisition H01J49/0036; detectors per se G01T, e.g. G01T1/28, G01T1/29
• CPC Class Codes: H01J 49/40 Time-of-flight spectrometers H01J49/36 takes precedence

Abstract

Ion injection in a drift tube apparatus for mobility spectrometry was accomplished without conventional ion shutters such as the Bradbury-Nielson or similar designs common to such drift tubes. Instead ions were passed between the ion source and drift region by using time-dependent electric field gradients that act as ion barriers between ordinary drift rings. Benefits of this design are simplicity and mechanical robustness. This ion injection technique dynamically accumulates the ions prior to their release into the drift region of the apparatus instead of destroying the ions created between shutter grid pulses, as does the Bradbury-Nielson method. The invention provides not only structural improvements to the well known drift tube apparatus, but also provides inventive methods for operating a drift tube apparatus to achieve maximum analyte injection efficiency and improving ion detection sensitivity. Improving ion detection sensitivity of drift tubes has practical experimental application. Incorporation of the inventive apparatus into a smoke detector is a further practical application of the invention.

Claims

1. An ion barrier mobility spectrometer apparatus, comprising:

a) an ion source;

b) a plurality of electrodes;

c) means for creating an electric field gradient between at least two of said plurality of electrodes;

d) means for creating an ion barrier at a downstream location of said electric field gradient;

e) said ion barrier positioning said ions;

f) means for adjusting the configuration of said ion barrier;

g) means for releasing said positioned ions from said ion barrier; and

h) a detector for detecting said released ions.

2. The apparatus of claim 1 wherein said means for releasing positioned ions simultaneously causes the collection of ions.

3. The apparatus of claim 1, further comprising means for shielding said detector.

4. An ion barrier mobility spectrometer apparatus comprising:

a) a source electrode;

b) a source shield electrode;

c) said source electrode and said source shield electrode operating at similar voltages;

d) an ion barrier electrode downstream from said source electrode, said ion barrier electrode operating at a relative voltage so as to create an ion barrier at a downstream end of an electric field gradient;

e) said ion barrier further positioning said ions;

f) means for releasing said positioned ions from said ion barrier; and

g) a detector for detecting said released ions.

5. The apparatus of claim 4, wherein said means for releasing positioned ions simultaneously causes the collection of ions.

6. The apparatus of claim 4, further comprising means for adjusting the configuration of said ion barrier.

7. The apparatus of claim 4, further comprising means for shielding said detector.

8. An ion barrier mobility spectrometer apparatus, comprising:

a) a first source shield electrode;

b) a second source electrode downstream from said source shield electrode;

c) said source electrode and said source shield electrode operating at similar voltages;

d) a third collection well electrode downstream from said source electrode;

e) a fourth electrode downstream from said third electrode;

f) a fifth trigger well electrode downstream from said fourth electrode;

g) a plurality of electrodes downstream from said fifth electrode, said plurality of electrodes together comprising a means for creating a decreasing voltage gradient; and

h) a detector downstream from said plurality of electrodes.

9. The apparatus of claim 8, further comprising means for shielding said detector

10. The apparatus of claim 8, used in a method for collecting and releasing ions, the method comprising:

a) first providing a voltage at said third electrode lower than voltages at said second and fourth electrodes; and

b) secondly increasing said voltages at said third and fourth electrodes above a voltage at said fifth electrode until the voltage generated across said fifth electrode forms a nearly vertical ion barrier.

11. The method of claim 10, wherein said voltage at said fourth electrode is minimized and said voltage at the third electrode is maximized to achieve said nearly vertical ion barrier.

12. The method of claim 10, wherein said fourth electrode is minimized at 200V, said third electrode is maximized at 300V and said fifth electrode is set at 100V to achieve said nearly vertical ion barrier.

13. A method to predict sensitivity improvement for ion detection in a drift tube apparatus, comprising:

a) introducing a plurality of ions at an upstream location of an electric field gradient;

b) creating an ion barrier at a downstream location of said electric field gradient;

c) measuring a quantity of time required for each of said plurality of ions to travel from said upstream location to said ion barrier;

d) adding up the quantity of time measured in step (c) for all of said plurality of ions to obtain a sum total, said sum total representing a relative value; and

e) comparing said relative value to a second relative value to create a ratio, said ratio representing a sensitivity improvement for ion detection.

14. A smoke detector comprising a sensing means which operates by sensing a reduction in detected reactant ions reaching a detector.

15. The smoke detector of claim 14, wherein said reactant ions are charged water clusters.

16. A smoke detector comprising an ion barrier mobility spectrometer apparatus.