Ion selecting device for identification of ions in gaseous media

• US 10,458,946 B2
• Filed: 03/13/2018
• Issued: 10/29/2019
• Est. Priority Date: 03/16/2017
• Status: Active Grant

• Current Assignee: Mobility Ion Technologies SL
• Original Assignee: Ancon Technologies Limited
• Inventors: Gorbunov, Boris Zachar
• Primary Examiner(s): Nguyen, Kiet T
• Application Number:
  US15/919,582
• Publication Number:
  US 20180266990A1
• Time in Patent Office: 595 Days
• Field of Search: 250286, 250287, 250283
• 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 49/061 Ion deflecting means, e.g. ion gates

Abstract

The invention provides a method of separating and collecting ions of a predetermined ion mobility from a gaseous mixture of ions of different ion mobilities using a differential mobility analyser apparatus, wherein the differential mobility analyser apparatus comprises an ion-separation chamber having:

• • (a) a sample gas flow inlet;
  • (b) a focusing chamber, an opening at one end of which serves as the sample gas flow inlet through which sample gas can flow into the ion-separation chamber;
  • (c) a sheath gas inlet connected or connectable to a supply of sheath gas;
  • (d) a sheath gas outlet;
  • (e) an ion outlet through which the ions of predetermined ion mobility can be collected; and
  • (f) two or more electrodes arranged to provide an ion-separating electric field across the ion-separation chamber;
    wherein the focusing chamber is oriented at an angle of from 30° to 90° relative to a direction of flow of the sheath gas along the ion-separation chamber;
    and wherein a focusing zone is provided in the focusing chamber, the focusing zone comprising at least two surfaces where a non-uniform density of electric charge can be created;
    the method of separating and collecting ions of predetermined ion mobility comprising:
• (i) introducing a stream of sheath gas through the sheath gas inlet at a predetermined flow rate;
• (ii) introducing a stream of sample gas containing an ion cloud into and through the focusing chamber and through the focusing zone therein at a predetermined flow rate;
• (iii) subjecting the ion cloud in the sample gas in the focusing zone to a non-uniform electric field generated by the non-uniform density of electric charge such that the electric field modifies ion trajectories in the sample gas so that they converge to produce an ion stream of reduced width;
• (iii) directing the stream of sample gas containing the ion stream of reduced width from the focusing chamber through the sample gas flow inlet into the ion-separation chamber; and
• (iv) selecting a field strength for the ion-separating electric field so as to attract ions of a predetermined ion mobility to the ion outlet.

Also provided is differential mobility analyser apparatus for separating and collecting ions of a predetermined ion mobility from a gaseous mixture of ions of different ion mobilities using a differential mobility analyser apparatus, wherein the differential mobility analyser apparatus comprises an ion-separation chamber having:

• • (a) a focusing chamber connected or connectable to a supply of sample gas containing ions of interest;
  • (b) a sheath gas inlet connected or connectable to a supply of sheath gas;
  • (b) a sheath gas outlet;
  • (c) an ion outlet through which the ions of predetermined ion mobility can be quantified or collected; and
  • (d) two or more electrodes arranged to provide an ion-separating electric field across the ion-separation chamber;
    wherein the sample gas inlet is oriented at an angle of from 30° to 90° relative to a direction of flow of the sheath gas along the ion-separation chamber;
    and wherein the apparatus is configured to provide a focusing zone in the focusing chamber, the focusing zone comprising at least two surfaces where a non-uniform density of electric charge is created so as to generate a non-uniform electric field that modifies ion trajectories in a sample gas passing through the focusing chamber and through the focusing zone so that they converge to produce an ion stream of reduced width;
    the apparatus comprising a controller that enables the ion-separating electric field to be varied to attract ions of a predetermined ion mobility to the ion outlet.

Claims

1. A method of separating and collecting ions of a predetermined ion mobility from a gaseous mixture of ions of different ion mobilities using a differential mobility analyser apparatus, wherein the differential mobility analyser apparatus comprises an ion-separation chamber having:

(a) a sample gas flow inlet;

(b) a focusing chamber, an opening at one end of which serves as the sample gas flow inlet through which sample gas can flow into the ion-separation chamber;

(c) a sheath gas inlet connected or connectable to a supply of sheath gas;

(d) a sheath gas outlet;

(e) an ion outlet through which the ions of predetermined ion mobility can be collected; and

(f) two or more electrodes arranged to provide an ion-separating electric field across the ion-separation chamber;

wherein the focusing chamber is oriented at an angle of from 30°

to 90°

relative to a direction of flow of the sheath gas along the ion-separation chamber;

and wherein a focusing zone is provided in the focusing chamber, the focusing zone comprising at least two surfaces where a non-uniform density of electric charge can be created;

the method of separating and collecting ions of predetermined ion mobility comprising;

(i) introducing a stream of sheath gas through the sheath gas inlet at a predetermined flow rate;

(ii) introducing a stream of sample gas containing an ion cloud into and through the focusing chamber and through the focusing zone therein at a predetermined flow rate;

(iii) subjecting the ion cloud in the sample gas in the focusing zone to a non-uniform electric field generated by the non-uniform density of electric charge such that the electric field modifies ion trajectories in the sample gas so that they converge to produce an ion stream of reduced width;

(iii) directing the stream of sample gas containing the ion stream of reduced width from the focusing chamber through the sample gas flow inlet into the ion-separation chamber; and

(iv) selecting a field strength for the ion-separating electric field so as to attract ions of a predetermined ion mobility to the ion outlet.

2. A method according to claim 1 wherein the differential mobility analyser apparatus is configured and set up in accordance with a first convoluting criterion that defines the relationship between the sample gas flow rate, sheath gas flow rate, the length of the ion-separation separation chamber and the width of the focusing chamber as follows:

(Hin/L)*(Qsh/Qi)>

Pf

where Hin is the width of the focusing chamber, L is the length of the ion separation chamber, Qsh is the sheath gas flow rate, Qi is the sample gas flow rate and Pf is a focusing factor which lies within the limits 1<

Pf<

30.

3. A method according to claim 1 wherein the focusing chamber is oriented at an angle of from 45°

to 90°

relative to the direction of flow of the sheath gas along the ion-separation chamber.

4. A method according to claim 3 wherein the focusing chamber is oriented at an angle of approximately 90°

relative to the direction of flow of the sheath gas along the ion-separation chamber.

5. A differential mobility analyser apparatus for separating and collecting ions of a predetermined ion mobility from a gaseous mixture of ions of different ion mobilities using a differential mobility analyser apparatus, wherein the differential mobility analyser apparatus comprises an ion-separation chamber having:

(a) a focusing chamber connected or connectable to a supply of sample gas containing ions of interest;

(b) a sheath gas inlet connected or connectable to a supply of sheath gas;

(b) a sheath gas outlet;

(c) an ion outlet through which the ions of predetermined ion mobility can be quantified or collected; and

(d) two or more electrodes arranged to provide an ion-separating electric field across the ion-separation chamber;

wherein the sample gas inlet is oriented at an angle of from 30°

to 90°

relative to a direction of flow of the sheath gas along the ion-separation chamber;

and wherein the apparatus is configured to provide a focusing zone in the focusing chamber, the focusing zone comprising at least two surfaces where a non-uniform density of electric charge is created so as to generate a non-uniform electric field that modifies ion trajectories in a sample gas passing through the focusing chamber and through the focusing zone so that they converge to produce an ion stream of reduced width;

the apparatus comprising a controller that enables the ion-separating electric field to be varied to attract ions of a predetermined ion mobility to the ion outlet.

6. A differential mobility analyser apparatus according to claim 5 which is configured and set up in accordance with a first convoluting criterion that defines the relationship between a sample gas flow rate, sheath gas flow rate, the length of the ion-separation chamber and the width of the focusing chamber as follows:

(Hin/L)*(Qsh/Qi)>

Pf

where Hin is the width of the focusing chamber, L is the length of the ion separation chamber, Qsh is the sheath gas flow rate, Qi is the sample gas flow rate and Pf is a focusing factor which lies within the limits 1<

Pf<

30.

7. A differential mobility analyser apparatus according to claim 5 wherein the focusing chamber is oriented at an angle of from 45°

to 90°

relative to the direction of flow of the sheath gas along the ion-separation chamber.

8. A differential mobility analyser apparatus according to claim 7 wherein the focusing chamber is oriented at an angle of approximately 90°

relative to the direction of flow of the sheath gas along the ion-separation chamber.

9. A differential mobility analyser apparatus according to claim 5 wherein the focusing chamber is provided with an electrically conductive strip located in a wall thereof, wherein the electrically conductive strip has a potential difference Δ

Vin applied thereto, thereby to generate a focusing electric field, the strip being insulated by a surrounding electrical insulator from any other internal conductive surfaces of the focusing chamber.

10. A differential mobility analyser apparatus according to claim 5 wherein the focusing chamber is provided with a plurality of electrically conductive strips located in a wall thereof, wherein each electrically conductive strip has a potential difference Δ

Vin applied thereto, thereby to generate a focusing electric field, each strip being insulated by a surrounding electrical insulator from any other conductive strips and internal conductive surfaces of the focusing chamber.

11. A differential mobility analyser apparatus according to claim 5 wherein the focusing chamber is provided on an internal surface thereof with a layer of a conductive material which is insulated from the electrodes of the ion-separation chamber by an electrical insulator material and wherein a pair of conductive electrodes is connected to the conductive material and said electrodes are in turn connected to a potential difference source so as to create a desired potential along the internal surface of the focusing chamber.

12. A differential mobility analyser apparatus according to claim 11 wherein the layer of conductive material is formed from a layer of metal or a metal alloy.

13. A differential mobility analyser apparatus according to claim 12 wherein the layer of conductive material is formed from a nickel alloy.

14. A differential mobility analyser apparatus according to claim 13 wherein the nickel allow is a nickel chromium alloy.

15. A differential mobility analyser apparatus according to claim 11 wherein the layer of conductive material has been formed by application of conductive material to a substrate by means of metal-plating, vacuum deposition or painting with a conductive paint.

16. A differential mobility analyser apparatus according to claim 5 wherein the two or more electrodes (d) are formed from stainless steel and are spaced apart by a PTFE spacer.

17. A differential mobility analyser apparatus according to claim 5 wherein a baffle (guide wall) is provided adjacent the ion outlet in the ion-separation chamber, the baffle serving to guide sample gas containing ions of a predetermined ion mobility to the ion outlet.