Method and apparatus for chemical ionization of a gas mixture

• US 10,224,190 B2
• Filed: 02/24/2016
• Issued: 03/05/2019
• Est. Priority Date: 02/25/2015
• Status: Active Grant

• Current Assignee: Universitat Innsbruck
• Original Assignee: Universitat Innsbruck
• Inventors: Breitenlechner, Martin, Hansel, Armin
• Primary Examiner(s): Ippolito, Nicole
• Application Number:
  US15/552,872
• Publication Number:
  US 20180047550A1
• Time in Patent Office: 1,105 Days
• Field of Search: 250281, 250282, 250288, 250423 R, 250424
• CPC Class Codes: G01N 30/7206 interfaced to gas chromatograph interfaces in general for introducing or extracting samples to be analysed with specially adapted mass spectrometer, see H01J49/04
• CPC Class Codes: H01J 49/0027 Methods for using particle spectrometers
• CPC Class Codes: H01J 49/06 Electron- or ion-optical arrangements
• CPC Class Codes: H01J 49/145 using chemical ionisation

Abstract

A method and apparatus for chemical ionization of analyte gas particles in a carrier gas by introducing primary ions, characterized in that the primary and product ions are accelerated by a rotating electric field orthogonal to that direction (5) in which the ions are transported towards the exit (3) of the reaction volume (1). This can, for example, reduce unwanted cluster formation without increasing the transport speed of the ions through the reaction chamber, which improves, for example, the product ion yield. The apparatus of the invention achieves this by means of N≥3 rod electrodes (6) to which N AC voltages U₁(t), . . . , U_N(t) with N different phase positions ascending in one sense of rotation φ₁, . . . , φ_N are applied.

Claims

1. A method for chemical ionization of a gas mixture by ion-atom reactions or ion-molecule reactions, wherein the gas mixture comprises at least one main component or a carrier gas and one or more reactant gases or analytes, wherein ionization is carried out by reactions with primary ions additionally introduced into the gas mixture, such that product ions are generated from neutral atoms or molecules of the reactant gases, the method comprising:

(a) introducing the gas mixture into a reaction volume having a central line parallel to an axial direction and orthogonal to a radial direction and a radial plane,

wherein the reaction volume comprises a first top surface, a second top surface and a lateral surface extending between the two top surfaces and wherein the central line extends from the first top surface to the second top surface and completely within the reaction volume;

(b) introducing primary ions suitable for the chemical ionization of the one or more reactant gas components into the reaction volume;

(c) accelerating the primary ions and generated product ions in the reaction volume by means of a temporally periodic electric field E(x,t),

(d) wherein E(x,t) has a radial field vector component E_r(Z,t) which, at all points {Z} lying on the central line, is orthogonal to the central line and which rotates periodically making exactly a 360°

rotation in the radial plane during the cycle duration T, and the absolute value |E_r(Z,t)| of which is unequal to zero in more than 80% of the times lying within a cycle duration T,

(e) wherein E(x,t) has an axial field vector component E_axi(Z,t) which, at all points {Z} lying on the central line, is parallel with respect to the central line and the absolute value |E_axi(Z,t)| of which is smaller than the absolute value of the rotating radial component |E_r(Z,t)|, and

(f) wherein t is time, x is a position vector, Z is a position vector of a point lying on the central line, {Z} is a set of all position vectors Z belonging to the central line, and T is the cycle duration of a 360°

rotation of E_r(Z,t).

2. The method according to claim 1, wherein the absolute value |E_r(Z,t)| varies at all points {Z} on the central line by at most 50% of its maximum value E_max(Z) in more than 80% of the times lying within a cycle duration T.

3. The method according to claim 1, wherein the absolute value |E_r(Z,t)| varies over at least 80% of the length of the central line by at most 50% of its maximum value.

4. The method according to claim 1, wherein rotation of the radial field vector component E_r(Z,t) corresponds to a harmonic circular motion so that, when shown in Cartesian coordinates (X,Y) being at the respective point Z orthogonal to the central line, E_r(Z,t) meets the following equation:

E_r(Z,t)=u_x·

[A_x(Z,t)·

sin(ω

t+Φ

₀)]+u_y·

[A_y(Z,t)·

cos(ω

t+Φ

₀)],

wherein u_x is the unit vector of the X-coordinate and u_y is the unit vector of the Y-coordinate, ω

is the angular frequency of rotation, Φ

₀ is a global phase offset, and

wherein the absolute value |E_r(Z,t)| varies by at most ±

10%.

5. The method according to claim 1, wherein the absolute value |E_r(Z,t)| of the rotating field vector E_r(Z,t) is unequal to zero and deviates by at most ±

10% from its average value E₀ being averaged in terms of time and location at all times t and at all points {Z} lying on the central line, and

wherein the axial field component E_axi(Z,t) is equal to zero at all times.

6. An apparatus for chemical ionization of a gas mixture by ion-atom reactions or ion-molecule reactions, wherein the gas mixture comprises at least one main component or a carrier gas and one or more reactant gases or analytes, wherein ionization is carried out by reactions with primary ions additionally introduced into the gas mixture, such that product ions are generated from neutral atoms or molecules of the reactant gases, the apparatus comprising:

(a) a reaction volume having a central line parallel to an axial direction and orthogonal to a radial direction and a radial plane, wherein the volume comprises a first top surface, a second top surface and a lateral surface extending between the two top surfaces and wherein the central line extends from the first top surface to the second top surface and completely within the reaction volume;

(b) N electrodes, wherein N is an integer larger than or equal to three, wherein each of the N≥

3 electrodes is arranged such that it extends from the boundary of the first top surface to the boundary of the second top surface and snuggles from the outside to the reaction volume so that it contacts the lateral surface along its overall extension being tangent to it from the outside,

(c) an AC voltage source which can be electrically connected to each of the N≥

3 electrodes, wherein the AC voltage source is configured such that a periodic AC voltage U_i(t) can be applied to each of the N≥

3 electrodes, wherein

U_i(t) is the AC voltage at the i-th electrode, wherein

the AC voltages U_i(t) to U_N(t) each have the same cycle duration T or the same frequency f=1/T, wherein

all AC voltages U_i(t) have a different phase position φ

_i between 0° and

360°

so that each voltage U<sub>i>

1</sub>(t) is temporally shifted with respect to the first voltage U₁(t) by the fraction Δ

t_i=(φ

_i/360°

)·

T of the cycle duration T, and wherein,

when the electrodes are numbered consecutively along the boundary of a top surface in a sense of rotation, the phase positions φ

_i and Δ

t_i are arranged in ascending order, i.e.

φ

₁=0°

<

φ

₂<

. . . <

φ

_i<

. . . <

φ

_N<

360°

, and

Δ

t₁=0<

Δ

t₂<

. . . <

Δ

t_i<

. . . <

Δ

t_N<

T.

7. The apparatus according to claim 6, characterized in that the N≥

3 electrodes are arranged such that in each radial plane an in-circle can be inscribed into them and the arrangement of the N electrodes divides this in-circle in equally-sized segments of a circle having an opening angle of 360°

/N, wherein

the electrodes are configured and arranged such that each section through the electrode configuration being orthogonal to the central line is rotationally invariant with respect to a rotation by 360°

/N.

8. The apparatus according to claim 6, wherein the phase positions φ

_i and Δ

t_i of the N AC voltages U_i(t) meet the following equations

φ

_i=[(i−

1)/N]·

360° and

Δ

t_i=[(i−

1)/N]·

T,

wherein the same phase difference φ

_i,i+1=[φ

<sub>i−

1</sub>−

φ

_i]=360°

/N and Δ

t_i,i+1=[Δ

t_i+1−

Δ

t_i]=T/N is present between all two neighboring electrodes.

9. The apparatus according to claim 6, wherein the AC voltages U_i(t) are substantially sinusoidal and at any time t deviate by at most ±

20% from the sine function U_i(t)=U₀*sin(ω

t+φ

_i).

10. The apparatus according to claim 6, wherein the central line is bent, or is closed, wherein, in case of a closed central line, the first top surface and the second top surface coincide in one surface.

11. The apparatus according to claim 6, wherein a cross-section through the lateral surface which is orthogonal to the central line changes in the course of the lateral surface from the first top surface to the second top surface.

12. The apparatus according to claim 6, wherein the electrodes and the AC voltage source are configured such that a static electric field can be applied within the reaction volume.

13. The apparatus according to claim 6, wherein the apparatus comprises, in addition to the electrodes, also further electrodes to which DC and/or AC voltages can be applied.

14. The apparatus according to claim 6, wherein the frequency f of the AC voltages U_i(t) ranges between 100 kHz and 100 MHz, the amplitudes U₀ of the AC voltages U_i(t) range between 50 V and 10 kV, the gas pressure p of the gas mixture in the reaction volume ranges between 10 mbar and 1 bar, the length L of the reaction volume measured along the central line ranges between 5 mm and 100 mm, and the inner diameter D of the reaction volume ranges between 1 mm and 20 mm.