METHOD AND DEVICE FOR DETECTION AND IDENTIFICATION OF GASES

• US 20100314548A1
• Filed: 01/12/2009
• Published: 12/16/2010
• Est. Priority Date: 01/19/2008
• Status: Active Grant

• Current Assignee: Airsense Analytics GmbH
• Original Assignee: Airsense Analytics GmbH
• Inventors: Ungethüm, Bert, Münchmeyer, Wolf, Walte, Andreas
• Granted Patent: US 9,404,889 B2
• Time in Patent Office: Days
• US Class Current: 250/375
• CPC Class Codes: G01N 27/622 Ion mobility spectrometry
• CPC Class Codes: G01N 27/624 Differential mobility spectrometry [DMS]; Field asymmetric-waveform ion mobility spectrometry [FAIMS]
• CPC Class Codes: H01J 49/0027 Methods for using particle spectrometers
• CPC Class Codes: H01J 49/0031 Step by step routines describing the use of the apparatus H01J49/0081 takes precedence

Abstract

It is an object of the invention to develop a generic method for identification of gases and a corresponding device, which has a simple structure and allows immediate and simultaneous detection of the chemical compounds to be tested, and which uses for identification the material-specific mobility and simultaneously the change in this mobility as a function of the electric field strength.

This is achieved in that due to the resulting electric field, each ionized molecule has a drift velocity which is partially increased or decreased, wherein the resulting electric field is a DC field, on which an asymmetric AC field is superimposed.

These methods and associated devices for the detection and identification of gases are used to identify and detect chemical compounds, in particular explosive and/or unhealthy substances or compounds, which must be detected in very small concentrations.

Claims

1. Method for identification of gases, wherein the gases to be identified are ionized and the drift times of the ionized molecules through a drift space (6) are measured and the measured drift times are evaluated, wherein for measurement of the drift times the ionized molecules are accelerated by a resulting electric field to drift velocities, wherein each ionized molecule has a drift velocity caused by the resulting electric field, which is partially increased or decreased, wherein the resulting electric field is a DC voltage field, on which an asymmetric AC field is superimposed, so that the ionized molecules perform a drift movement in one direction, with the oscillatory movement superimposed parallel thereto.

2. Method according to claim 1, wherein the change in the drift velocity is due to the fact that each ionized molecule performs due to the resulting electric field a constant drift movement on which an oscillatory movement is superimposed.

3. Method according to claim 1, wherein positive and/or negative ions are used as ionized molecules.

4. Method according to claim 1, wherein each ionized molecule is accelerated and decelerated several times, wherein on average, depending on the material properties of the molecule, the acceleration is greater or smaller than the deceleration.

6. Method according to claim 1, wherein the DC voltage field has a low electric field strength, and the asymmetric AC voltage field has a high electric field strength.

7. Method according to claim 6, wherein the amplitude of the asymmetric AC voltage is changed during the measurement of the drift times.

8. Method according to claim 1, wherein identification of the chemical compounds the measured drift times are compared with previously determined drift times of known chemical compounds.

9. Method according to claim 8, wherein the comparison between the measured drift times and the known drift times of chemical compounds is performed using mathematical or statistical methods, in particular rule-based algorithms or artificial neural networks.

10. Method according to claim 1, wherein the drift times of ionized molecules having identical mobilities at low electric field strengths are compared with the drift times of these ionized molecules after the asymmetric AC voltage field with a high electric field strength generated by the AC voltage electrodes (12) is switched in, and that for identification of the chemical compounds these measured drift times are compared with the previously determined drift times.

5. (canceled)

11. Device for identification of gases, comprising an inlet system (2) and at least one detector (3), wherein at least one drift tube (1) is delimited, on one hand, by the inlet system (2) and, on the other hand, by a corresponding detector (3), and that in each drift tube (1) an opening and closing grid (4) is disposed which divides the drift tube (1) into a reaction space (5) and a drift space (6), wherein an ion source (7) is arranged in the reaction space (5) and a shield grid (8) is arranged in the drift space (6), wherein the drift tube (1) comprises several DC voltage electrodes (11) and AC voltage electrodes (12) arranged around the drift space (6).

12. Device according to claim 11, wherein an additional drift tube (1) is delimited, on one hand, by the inlet system (2) and, on the other hand, by an additional detector (3), wherein the drift tubes (1) have opposite polarities.

13. Device according to claim 11, wherein the drift tube (1) comprises alternatingly arranged metal rings (9) and isolator rings (10), wherein each metal ring (9) is electrically connected around the drift space (6) and forms a respective DC voltage electrode (11).

14. Device according to claim 11, wherein the drift tube (1) comprises one or more tubes with low electric conductivity.

15. Device according to claim 11, wherein the AC voltage electrodes (12) are distributed along the length of the drift space (6) and comprise thin wire grids extending transversely through the drift space (6).

16. Device according to claim 11, wherein the opening and closing grid (4) comprises two electrically conducting metal combs (13), which are arranged in a plane extending transversely through the drift tube (1), wherein the metal combs (13) are slightly offset from one another and do not contact each other.

17. Device according to claim 16, wherein the opening and closing grid (4) has two switching states, wherein:

in a first switching state, the opening and closing grid (4) is closed, because the metal combs (13) are at different potentials and this potential difference produces a high field strength, thereby preventing ions from passing through the opening and closing grid (4), and

in a second switching state, the opening and closing grid (4) is open, because the metal combs (13) are at the same potential, so that no electric field at all or only an electric field with a low field strength is produced, allowing ions to pass through the opening and closing grid (4).

18. Device according to claim 11, wherein the shield grid (8) is arranged in front of the detector (3), wherein the shield grid (8) provides capacitive decoupling.

19. Device according to claim 11, wherein the drift tube (1) comprises at least one auxiliary electrode (18) which is arranged in the drift space (6) for generating an additional compensation voltage.

20. Device according to claim 11, wherein the drift tube (1) comprises at least three AC voltage electrodes (12) in the drift space (6) and that the drift tube (1) is preferably constructed as a circular cylinder.