WO2003040682A2

WO2003040682A2 - Ion mobility spectrometer with specifically adapted ion gate

Info

Publication number: WO2003040682A2
Application number: PCT/EP2002/012467
Authority: WO
Inventors: Jörg Ingo BAUMBACH; Hartwig Schmidt; Wong Jong Kang; Markus Teepe
Original assignee: Gesellschaft Zur Förderung Der Spektrochemie Und Angewandte Spektroskopie E.V.
Priority date: 2001-11-09
Filing date: 2002-11-08
Publication date: 2003-05-15
Also published as: AU2002357497A1; DE10155259C1; WO2003040682A3

Abstract

The aim of the invention is to essentially reduce the size of ion gates for an ion mobility spectrometer, with the simplest possible construction and retaining full functionality, on an ion mobility spectrometer comprising an ionisation chamber with gas inlets and outlets, an ionisation source and a drift chamber, whereby the ionisation chamber and the drift chamber are separated by an ion gate which has electrodes with differing, variable electric potentials. Said aim is achieved, whereby the ion gate (6) has an external annular electrode (16) and an inner electrode (17), which is centrally arranged relative to the axis of symmetry of the ion mobility spectrometer.

Description

"Ion mobility spectrometer"

The invention relates to an ion mobility spectrometer with an ionization chamber with gas inlet and outlet as well as an ionization source and with a drift space, the ionization space and the drift space being separated from one another by an ion gate which has electrodes with mutually different, changeable electrical potential.

Ion mobility spectrometry has continuously developed as an analytical method for the characterization of traces of gases or gas mixtures in air or other carrier gases (ng to pg, ppm _v to ppt _? Range) at ambient pressure over the past decades. Initially, the focus was on military applications for the detection of chemical warfare agents or explosives, so the range of applications quickly expanded to include areas such as drug detection, process control in the synthesis of volatile organic compounds and trace analysis of airborne organic components as well as the detection of peptides, biomolecules and bacteria. Well-known application examples are the gas warning systems for the Reichstag building in Berlin based on ion mobility spectrometry or the ion mobility spectrometers for explosives and drug detection that can be found at more and more international airports via a coupling with thermodesorption. The ion mobility spectrometry is based on the suitable ionization of a gaseous analyte (for example with radioactive radiation, UV light (8.5 to 11.8 eV) or with electrical discharges) and subsequent separation of the positive or negative ions thus formed in a drift tube at ambient pressure and often also at ambient temperature. For this purpose, swarms of ions for short lattice opening times (usually 10 μs to 1 ms) enter drift tubes of a few cm in length and are ideally separated in electrical fields by 300 Vcm ^"1. For exact determination of the starting point of the ions at the ion gate and for protection against the When analyte molecules enter the drift space, a drift gas is often used, which counteracts the ions drifting in the direction of a Faraday plate arranged at the end of the drift space facing away from the ion gate Unlike prevails to the mass spectrometer atmospheric pressure, determined not only by the mass of the ions and the number of collisions with neutral molecules, the drift time. Thus, the molecular structure plays an important role. In this way, isomers can be separated what _the. method, for example for peptide analysis, interesting makes.

The time it takes for the ions to go through a need a certain drift path in an electric field that is as homogeneous as possible is inversely proportional to the mobility of the ions. Under certain conditions, the analytes can be identified via the mobility.

As mentioned above, the ion gate is essential for the functionality of the ion mobility spectrometer. The most commonly used arrangement of the grating is the so-called Bradbury-Nielsen grating, which realizes a transverse field by giving an increased and / or a decreased value to an external potential in accordance with an impressed electric field, so that the transverse field is larger than the longitudinal field in the drift tube and the ions from the ionization space cannot penetrate through the grid into the drift space. If these potentials coincide with the imprinted value, the grating works as a field stabilization ring and is briefly permeable to ions for the respective short measuring process.

The configurations of such ion gates used to date are mentioned, for example, in EP 0 027 748 AI. The grid is formed by parallel wires, which are connected in pairs in such a way that one increases and the other the reduced potential gets embossed. This normal state (closed grid), in which no ions can penetrate from the ionization space into the drift space, is then brought into the state permeable to ions by the rectangular voltage-like collapse of the additional voltage to the potential represented by the longitudinal field at the location of the ion gate.

The manufacture of such ion gates is comparatively complex, the geometrical area for the discharge of impinging ions is high, and the ion yield is thus reduced. In addition, these gratings stand in the way of a desired miniaturization of ion mobility spectrometers, since gratings of this type, which have hitherto usually had a diameter of approximately 1.5 cm, are reduced by a power of 10, i.e. a reduction in the m range, are no longer permeable.

The object of the invention is to provide a solution with which ion gates for an ion mobility spectrometer can be significantly reduced while being fully functional and as simple as possible to manufacture.

This object is achieved according to the invention with an ion mobility spectrometer of the type described in the introduction in that the ion gate has an outer ring-shaped one Electrode and an inner electrode arranged with respect to the axis of symmetry of the ion mobility spectrometer.

With such a configuration of the ion gate, it is possible to significantly miniaturize an ion mobility spectrometer overall, for example, the ion gate with this configuration can be easily implemented with a diameter of approximately 2 mm. The outer annular electrode can have different shapes, for example circular, square, cruciform or the like. However, it should form an essentially closed ring. Such an ion gate can be easily manufactured in a mass production process, for example directly with PCB technology (printed circuit board technology) and PCB milling technology or in a mixture of PCB and wiring technology. The ion gate has extreme mechanical stability since there are no free-standing parts. There is also no noise and no microphone effect. In addition, the ion gate has a high level of electromechanical stability, since it is designed to be centrally symmetrical and thus self-stabilizing. Due to the smaller number of permeable surfaces in the ion flight direction compared to conventional ion gates, there is a higher relative yield of ions, since the wires themselves always have a certain reduction effect of the ion current.

In principle, the known grids and the ion gate according to the invention function analogously, in that a voltage pulse is suitably impressed. However, while the grids according to the prior art, because of the comparatively large diameter in the interior of the ion mobility spectrometer (reaction space and drift space), numerous wires remain in the interior of an ion mobility spectrometer so that the voltages to be regulated remain easily switchable (typical values are +50 V on 3 to 10 kV high voltage), miniaturizations of ion gates designed according to the invention can be realized without the need for higher reverse voltages. In some cases, these can even be significantly reduced.

In the ion gate designed according to the invention, the two electrodes in the basic state have a (V +) or reduced (V-) potential which is increased by a certain value compared to the potential according to the longitudinal field setting at the position of the grid, so that a potential gradient within the preferably cylindrical (drift -) tube and thus a cross-field is built. This blocking field, in which the ions can be applied to the outer ring-shaped wall electrode or to the inner center if the potential is selected appropriately. If the two electrodes assume the potential that is applied at the position of the grid according to the longitudinal field setting, the ion gate acts as a field stabilization ring and the ions of the corresponding polarity are let through into the drift space.

The inner electrode of the ion gate can basically be designed differently, provided that it is approximately symmetrical to the center. For example, the inner electrode can be cruciform or also as a ring with a web that is guided to the outside.

As already mentioned, the diameter of the outer ring-shaped electrode is approximately 1-5 mm, of course, other orders of magnitude can also be realized.

For example, the ion gate can be manufactured directly in two levels using PCB etching technology, i.e. the two electrodes are then arranged parallel to one another in two planes. From a manufacturing point of view, a cruciform structure in the middle of one side with a square counter electrode on the back of a circuit board is preferred.

In further development it is planned that the two Electrodes are arranged in one plane. As a result, the starting point of the ions is even better defined than in the aforementioned embodiment.

The invention is explained in more detail below with reference to the drawing. This shows in:

1 is a schematic diagram of an ion mobility spectrometer,

2 shows a basic illustration of an ion gate designed according to the invention,

Fig. 3 is an ion gate similar to the ion gate of Figure 2 in perspective and in

Fig. 4 shows a modified embodiment of an ion gate for an ion mobility spectrometer.

An ion mobility spectrometer 1 is usually tubular and initially has a tubular ionization chamber 2, in which an ionization source 3 is arranged. The ionization chamber 2 is provided with a gas inlet 4, indicated only by an arrow, through which gas molecules 5 to be analyzed enter the ionization chamber 2. The ionization space is 2 separated from a drift space 7 by an ion gate 6, at the other end of which a Faraday plate 8, possibly with an aperture grating 9, is arranged.

A gas outlet indicated by an arrow 10 is provided in the edge region of the ionization space 2 adjoining the ion gate 6. An electrical field is applied along the entire tubular ionization space 2 and drift space 7, which is indicated by an arrow 11.

In the edge region of both the ionization space 2 and the drift space 7, drift rings 12 can be arranged at a distance from one another. At the end of the drift space 7, adjacent to the Faraday plate 8, a drift gas inlet is provided, which is indicated by an arrow 13.

Such an ion mobility spectrometer 1 works in a known manner, ie the gas to be analyzed enters the ionization space 2 through the gas inlet 4, where different ions are generated by the ionization source 3, which are identified by the reference numerals 14 and 15. Because of the electric field 11, the ions 14, 15 are guided in the direction of the ion gate 6, which, however, is normally closed due to an electrical transverse field. Non-ionized gas as well Ions not passing through the ion gate 6 emerge again from the ion mobility spectrometer through the gas outlet 10. During a brief opening moment of the ion gate 6, in which the electrical transverse field existing in the ion gate 6 is briefly canceled, the ions 14, 15 can pass through the ion gate 6 and reach the drift space 7, where they move due to the electrical field 11 in the direction of the Faraday - Get plate 8. The grating opening times are usually 10 μs to 1 ms, the electric field has a strength of approximately 300 Vcπf ¹ . In order to prevent analyte molecules from penetrating into the drift space 7 when the ion gate 6 is opened, drift gas 13 is simultaneously fed into the drift space 7 in the opposite direction. This flows against the ions 14, 15 drifting in the direction of the Faraday plate 8. The time it takes for the ions 14, 15 to pass through the drift space 7 is inversely proportional to the mobility of the ions 14, 15. The analytes can thus be identified via the mobility.

Only the design of the ion gate 6 is essential for the configuration of the ion mobility spectrometer 1 according to the invention. A first configuration is shown in FIGS. 2 and 3. In this embodiment, the ion gate 6 initially has an outer annular one Electrode 16, which in the exemplary embodiment according to FIG. 2 is closed in a cross shape. Provided within this cruciform closed annular outer electrode 16 is an inner electrode 17 which is centered with respect to the axis of symmetry of the ion mobility spectrometer and is of cruciform design. Both electrodes 16, 17 each have a different electrical potential, the outer electrode 16, for example, the potential V + and the inner electrode 17 a negative potential V-.

In the embodiment according to FIG. 3, which essentially corresponds to the embodiment according to FIG. 2, a cruciform inner electrode 17 is likewise provided, in contrast the outer electrode 16 'is of approximately circular design. Both electrodes 16, 17 are arranged in one plane (also in the embodiment according to FIG. 2). In the embodiment according to FIG. 3, they are integrated in a circuit board 18.

In the embodiment according to FIG. 4, the outer electrode 16 is also ring-shaped, but in a square shape. The inner electrode 17 is in turn cruciform. In this embodiment, however, the two electrodes 16, 17 are not in one plane, but in two parallel planes at a distance d from one another. arranged one another. This results in an electric blocking field, which is shown in the right-hand illustration of FIG. 4. Such a grid 6 can be produced, for example, directly with PCB etching technology, with a cross-shaped structure of the inner electrode 16 in the middle of one side and a square outer counter electrode 16 on the back of a circuit board.

Such an ion gate 6 can be produced with extremely small dimensions, for example with a diameter of 1 to 5 mm, which enables a reduction by a power of 10 compared to known ion gates, so that overall a miniaturization of the entire ion movement with an ion gate 6 designed according to the invention spectrometer is enabled.

Of course, the invention is not restricted to the exemplary embodiments shown. Further configurations are possible without leaving the basic idea. For example, the inner electrode 16 also have a different shape, for example it can be in the form of a ring with an outwardly directed web, it is essential that it is formed approximately symmetrically to the center.

Claims

Claims;

1. Ion mobility spectrometer with an ionization chamber with gas inlet and outlet and an ionization source and with a drift chamber, the ionization chamber and the drift chamber being separated from one another by an ion gate which has electrodes with mutually different, changeable electrical potential, characterized in that the ion gate (6) has an outer annular electrode (16) and an inner electrode (17) which is arranged centered with respect to the axis of symmetry of the ion mobility spectrometer.

2. Ion mobility spectrometer according to claim 1, characterized in that the inner electrode (17) is cross-shaped.

3. ion mobility spectrometer according to claim 1 or 2, characterized in that the inner electrode (17) is designed as a ring with a web.

4. ion mobility spectrometer according to claim 1 or one of the following, characterized in that the diameter of the outer annular electrode

(16) is about 1-5 mm.

5. Ion mobility spectrometer according to claim 1 or one of the following, characterized in that the two electrodes (16, 17) are arranged in one plane.

6. ion mobility spectrometer according to one or more of claims 1 to 4, characterized in that the two electrodes (16, 17) in two parallel

Layers are arranged.