ION MOBILITY SPECTROMETER

Description

[0001] The invention relates to an ion mobility spectrometer with a tubular ionization chamber having a sample gas inlet and a gas outlet and with an ionization device arranged within the ionization chamber, as well as with a tubular drift chamber which is separated from the ionization chamber by an ion grid, wherein the drift chamber has an ion detector and a drift gas inlet at the end facing away from the ion grid, and wherein the ionization device is arranged on the end face of a cylindrical flow body arranged in the ionization chamber.

[0002] Such ion mobility spectrometers (IMS) are currently designed for maximum ionization and thus high sensitivity. This results in a long residence time of the sample in the ionization chamber of the ion mobility spectrometer. In modern systems with upstream gas chromatographic (GC) separation, this inevitably leads to a broadening of the detected signals (due to the decay of the efflux from the ionization chamber of the ion mobility spectrometer into which the substances separated in the gas chromatographic column elute). This results in a deterioration of the gas chromatographic separation. An ion mobility spectrometer with the features of the preamble of claim 1 is known from US 5,021,654 A.

[0003] Further ion mobility spectrometers without a cylindrical flow body are known from DE 10 2008 029 555 A1 and US 4 633 083 A.

[0004] The object of the invention is to create an ion mobility spectrometer that, in conjunction with a gas chromatographic pre-separation, ensures good gas chromatographic resolution.

[0005] This problem is solved according to the invention in an ion mobility spectrometer of the type described above by the fact that the ionization device has a planar contact surface which is aligned parallel to and at a small distance from the ion lattice transversely to the longitudinal axis of the ionization chamber, wherein the sample gas inlet has a sample gas supply line, the sample discharge end of which opens directly into the area of ​​the contact surface of the ionization device.

[0006] By introducing the sample directly into the ionization zone of the ion mobility spectrometer and by using the flow-through gas flow system, the residence time of the eluting sample can be specifically shortened and optimized. This reduction in residence time ensures good gas chromatographic resolution, thus fully realizing the advantages of coupling gas chromatographic pre-separation with an ion mobility spectrometer.

[0007] Furthermore, at very high drift gas to sample gas ratios, a targeted reduction in the sensitivity of the ion detector can be achieved. This results in a flattening of the calibration curve (detected substance signal vs. concentration), so that the maximum detectable concentration range – inherent to the IMS principle – can be significantly shifted upwards. This saturation of the detector, or its limited dynamic range, often represents a limitation in numerous analytical applications, which is significantly improved by the invention.

[0008] The planar contact surface of the ionization unit, arranged perpendicular to the drift tube, and the small distance to the electronic ion lattice further result in optimized IMS resolution. Combined with the improved GC resolution, this typically makes it possible to analyze complex mixtures of substances in a shorter measurement time or with improved analytical resolution. This is advantageous for analytical measurement tasks.

[0009] The design of the ion mobility spectrometer eliminates dead volume at the ionization unit, thus preventing the mixing of molecules separated in the GC column by low-flow zones upstream of the ionization unit. Ions are directly transported out of the working area by the electric field and the drift gas stream. Furthermore, forced ionization occurs through gas flow across the active area towards the gas outlet.

[0010] It is particularly preferred that each sample gas inlet and drift gas inlet is assigned a flow controller (e.g., an electronic pressure controller) to regulate the respective volumetric flow rate. This allows the ion current to be controlled by independently adjustable volumetric flow rates of the sample and drift gas. The volumetric flow rates can be set, for example, via the firmware of the ion mobility spectrometer.

[0011] In a preferred design, the sample gas supply line is integrated into the flow body. Alternatively, the sample gas supply line can also be designed separately from the flow body.

[0012] The sample gas supply line can preferably extend along the longitudinal axis of the ionization chamber.

[0013] Furthermore, it may be provided that the flow body is designed to taper conically from the ionization device.

[0014] It can also be advantageously provided that the tubular ionization chamber is conically tapered towards the end facing away from the ionic lattice.

[0015] The invention also relates to a measuring device with a previously described ion mobility spectrometer and with a gas chromatographic pre-separation connected to the sample gas inlet of the ion mobility spectrometer.

[0016] The invention is explained in more detail below with reference to the drawing.

[0017] This shows in Fig. 1 a schematic sectional view of an ion mobility spectrometer according to a first embodiment with a gas chromatographic pre-separation, Fig. 2 a schematic sectional view of an ion mobility spectrometer according to a second embodiment, Fig. 3 a schematic sectional view of an ion mobility spectrometer according to a third embodiment, Fig. 4 an ionization chamber of an ion mobility spectrometer according to a fourth embodiment in schematic sectional view and Fig. 5 an ionization chamber of an ion mobility spectrometer according to a fifth embodiment in schematic sectional view.

[0018] An ion mobility spectrometer is generally designated by 1. This ion mobility spectrometer 1 has a tubular housing 2, the longitudinal axis of which is designated by L.

[0019] The interior of the tubular housing 2 is divided into a tubular ionization chamber 4 and a tubular drift chamber 5 by an ionic grid 3 arranged transversely to the longitudinal axis L.

[0020] The ionization chamber 4 has a sample gas inlet 6 and a gas outlet 7, while the drift chamber 5 has a drift gas inlet 8 at the end of the drift chamber 5 opposite the ionic lattice 3. An ionization device 9, e.g., a UV radiation source or a radioactive radiation source, is arranged within the ionization chamber 4.

[0021] At the end opposite the ion grating 3, the drift chamber 5 has an ion detector 10, which can consist, for example, of a Faraday plate and an aperture grating arranged in front of this Faraday plate. During operation of the ion mobility spectrometer, a preferably homogeneous electric field is generated along the drift path in the drift chamber 5, for which purpose metal rings 11 integrated into the housing 2 and connected to a voltage source are provided.

[0022] The ion mobility spectrometer 1 described so far is generally known; according to the invention, it is now designed in the manner described in more detail below, in order to be used as a measuring device, in particular together with a gas chromatographic pre-separation.

[0023] Such a gas chromatographic pre-separation is used in Fig. 1schematically represented as a loop-shaped coiled line and labelled 12. This gas chromatographic pre-separation 12 is connected to the sample gas inlet 6 of the ion mobility spectrometer 1.

[0024] The ionization device 9 is arranged on the end face 14a of a cylindrical flow body 14 located in the ionization chamber 4. The ionization device 14 has a planar contact surface 14a, which is oriented at a small distance (approximately between 1 mm and 3 mm with an inner diameter of 15.2 mm for the ionization chamber) and parallel to the ionic lattice 3, perpendicular to the longitudinal axis L of the ionization chamber 4. Furthermore, the sample gas inlet 6 has a sample gas supply line 13, the sample gas discharge end 13a of which opens directly into the area of ​​the contact surface 9a of the ionization device 9.

[0025] In the Figs. 1 to 3In the illustrated embodiments, the sample gas supply line 13 is integrated into the flow body 14 and extends along the longitudinal axis L of the ionization chamber 4. The flow body 14 preferably has the longitudinal axis L as its axis of symmetry.

[0026] Both the sample gas inlet 6 and the drift gas inlet 8 are each assigned a flow controller 15, 16 for regulating the respective volume flow of the sample gas and the drift gas, respectively. The preferably electronic flow controller 15 is integrated into the corresponding supply line upstream of the gas chromatographic pre-separation 12 (viewed in the direction of flow), and the preferably also electronic flow controller 16 is integrated into the drift gas supply line 17, which leads into the drift gas inlet 8.

[0027] In the embodiment according to Fig. 1The flow body 14 is conically tapered from the ionization device 9, as is the tubular ionization chamber 4 towards the end facing away from the ion lattice 3. This results in flow conditions that are represented by arrow 18 for the drift gas flow and arrow 19 for the sample ion flow in the drift chamber 5.

[0028] In Fig. 2 A second embodiment of an ion mobility spectrometer 1 is shown, which differs from the one described above. Fig. 1 The only difference is that the geometric shape of the ionization chamber 4 and the flow body 14 is different; both are cylindrical in this embodiment. The gas chromatographic pre-separation 12 is in Fig. 2 not shown.

[0029] The embodiment according to Fig. 3 differs from the one after Fig. 1only because the ionization chamber 9 is cylindrical, while the flow body 14 is conically shaped.

[0030] In the fourth embodiment according to Fig. 4 The sample gas supply line is designed differently; it is not integrated into the flow body 14, but is essentially guided transversely to the longitudinal axis L as a hose or the like through the wall of the housing 2 to the center of the contact surface after the ionization device 9.

[0031] The embodiment of the Fig. 5 differs from the one after Fig. 4 only because the ionization device 9 extends only partially over the front face 14a of the flow body 14 and the sample gas supply line 13 opens at a slightly different point in the area of ​​the contact surface 9a of the ionization device 9. Reference symbol list :

[0032] 1 Ion mobility spectrometer 2 Housing 3 Ionic grid 4 Ionization chamber 5 Drift chamber 6 Sample gas inlet 7 Gas outlet 8 Drift gas inlet 9 Ionization unit 9a Contact surface 10 Ion detector 11 Metal rings 12 Gas chromatographic pre-separation 13 Sample gas inlet 13a Sample gas outlet 14 Flow body 14a End face 15 Flow regulator 16 Flow regulator 17 Drift gas inlet 18 Arrow 19 Arrow Longitudinal axis

Claims

1. Ion mobility spectrometer comprising a tubular ionization chamber (4) having a sample gas inlet (6) and a gas outlet (7), and having an ionization device (9) arranged within the ionization chamber (4), as well as a tubular drift chamber (5) which is separated from the ionization chamber (4) by an ion gate (3), wherein the drift chamber (5) has, at the end facing away from the ion gate (3), an ion detector (10) and a drift gas inlet (8), wherein the ionization device (9) is arranged at the front side (14a) of a cylindrical flow body (14) arranged in the ionization chamber (4), or of a flow body (14) tapering conically starting from the ionization device (9), which produces the third-gas flow guidance, characterized in that the ionization device (9) has a planar contact surface (9a) which is aligned parallel to and at a small distance from the ion gate (3) transverse to the longitudinal axis (L) of the ionization chamber (4), wherein the sample gas inlet (6) has a sample gas supply line (13), the sample discharge end (13a) of which opens directly in the region of the contact surface (9a) of the ionization device (9).

2. Ion mobility spectrometer according to claim 1, characterized in that a flow controller (15, 16) for controlling the respective volume flow is assigned to each of the sample gas inlet (6) and the drift gas inlet (8).

3. Ion mobility spectrometer according to claim 1 or 2, characterized in that the sample gas supply line (13) is integrated into the flow body (14).

4. Ion mobility spectrometer according to claim 3, characterized in that the sample gas supply line (13) extends along the longitudinal axis (L) of the ionization chamber (14).

5. Ion mobility spectrometer according to one of claims 1 to 4, characterized in that the tubular ionization chamber (4) is formed tapering conically toward the end facing away from the ion gate (3).

6. Measuring device comprising an ion mobility spectrometer (1) according to one or more of claims 1 to 5, and a gas-chromatographic pre-separation (12) connected to the sample gas inlet (6) of the ion mobility spectrometer (1).