Abstract
The present invention relates to the technical field of ionizing a gaseous substance, in particular the ionizing or ionization of a gaseous substance in preparation for its analysis. A device is intended to make a discharge gas and a test substance ionizable in a flow-through mode without essentially destroying or fragmenting the sample substance. In order to avoid a high expenditure in terms of construction and equipment, the device is intended to be usable under ambient conditions and to ensure a high sensitivity in a possible analysis of an ionized substance. To this end, an ionizing device is used for flow-through ionization of a discharge gas and of a sample substance at an absolute pressure of more than 40 kPa in the ionizing device during ionization. The ionizing device comprises an inlet, an outlet, a first electrode, a dielectric element and a second electrode. The dielectric element is configured in the shape of a hollow body having an inner side and an outer side and it allows a flow of the discharge gas and of the sample substance therethrough in a flow direction. The first electrode is arranged outside of the outer side of the dielectric element. The second electrode is arranged, at least sectionwise, inside the dielectric element, is surrounded by the inner side of the dielectric element perpendicularly to the flow direction, and allows a flow of the discharge gas and of the sample substance therethrough or therearound. A distance in or contrary to the flow direction exists between the associated ends of the first and second electrodes and lies between 5 mm to 5 mm. A dielectric barrier discharge is establishable in a dielectric barrier discharge region by applying a voltage between the first and second electrodes so as to ionize the discharge gas or the sample substance.
Claims
1. A method of flow-through ionization of a discharge gas and of a sample substance in an ionization device at an absolute pressure of more than 40 kPa in the ionizing device, during ionization, the ionizing device comprising an inlet, an outlet, a first electrode, a dielectric element and a second electrode, wherein: (a) the dielectric element is configured in the shape of a hollow body having an inner side and an outer side, and the discharge gas and the sample substance flow therethrough in a flow direction; (b) the first electrode is arranged outside of the outer side of the dielectric element; (c) the second electrode is arranged, at least sectionwise, inside the dielectric element, is surrounded by the inner side of the dielectric element perpendicularly to the flow direction, and the discharge gas and the sample substance flow therethrough or therearound; (d) a distance in or contrary to the flow direction between the associated ends of the first and second electrodes lies between 5 mm and 5 mm; (e) a dielectric barrier discharge is established in a dielectric barrier discharge region by applying a voltage between the first and second electrodes so as to ionize the discharge gas or the sample substance.
2. The method according to claim 1, wherein the pressure in the ionizing device is higher than 60 kPa, preferably higher than 80 kPa and is particularly preferred essentially atmospheric pressure.
3. The method according to claim 1, wherein the distance between the associated ends of the first and second electrodes lies between 3 mm and 3 mm, preferably between 1 mm and 1 mm, more preferably between 0.2 mm and 0.2 mm and most preferably between 0.05 mm and 0.05 mm.
4. The method according to claim 1, wherein the second electrode has the shape of a hollow cylinder, the shape of a longitudinally extending hollow body with a triangular, rectangular or oval basic shape, or is a wire.
5. The method according to claim 1, wherein the outer side of the second electrode is spaced apart from the inner side of the dielectric element at a distance of less than 0.5 mm, preferably less than 0.1 mm, and is preferably in contact with the inner side of the dielectric element.
6. The method according to claim 1, wherein the first electrode is substantially in contact with the outer side of the dielectric element and is preferably configured as a layer applied through a drying or curing liquid or suspension or is applied through a transition from a vapor phase into a solid phase.
7. The method according to claim 1, wherein the flow-through area of the outlet of the ionizing device is smaller than or equal to the area of the inlet of the ionizing device, and the outlet of the ionizing device has preferably arranged thereon a flow limitation unit.
8. The method according to claim 1, wherein a pressure gradient inside the ionizing device causes a flow with the flow direction in the ionizing device, preferably through a vacuum at the outlet and an essentially atmospheric pressure directly outside the inlet.
9. An ionizing device for flow-through ionization, comprising an inlet, an outlet, a first electrode, a dielectric element and a second electrode, wherein: (a) the dielectric element is configured in the shape of a hollow body having an inner side and an outer side, and allows a flow of a discharge gas and of a sample substance therethrough in a flow direction; (b) the first electrode is arranged outside of the outer side of the dielectric element; (c) the second electrode is arranged, at least sectionwise, inside the dielectric element, is surrounded by the inner side of the dielectric element perpendicularly to the flow direction, and allows a flow of the discharge gas and of the sample substance therethrough or therearound; (d) a distance in or contrary to the flow direction between the associated ends of the first and second electrodes lies between 5 mm and 5 mm; (e) a dielectric barrier discharge is establishable in a dielectric barrier discharge region by applying a voltage between the first and second electrodes so as to ionize the discharge gas or the sample substance; and (f) the absolute pressure in the ionizing device during an ionization is higher than 40 kPa.
10. The ionizing device according to claim 9, wherein the pressure in the ionizing device is higher than 60 kPa, preferably higher than 80 kPa and is particularly preferred essentially atmospheric pressure.
11. The ionizing device according to claim 9, wherein the distance between the associated ends of the first and second electrodes lies between 3 mm and 3 mm, preferably between 1 mm and 1 mm, more preferably between 0.2 mm and 0.2 mm and most preferably between 0.05 mm and 0.05 mm.
12. The ionizing device according to claim 9, wherein the second electrode has the shape of a hollow cylinder, the shape of a longitudinally extending hollow body with a triangular, rectangular or oval basic shape, or is a wire.
13. The ionizing device according to claim 9, wherein the outer side of the second electrode is spaced apart from the inner side of the dielectric element at a distance of less than 0.5 mm, preferably less than 0.1 mm, and is preferably in contact with the inner side of the dielectric element.
14. The ionizing device according to claim 9, wherein the first electrode is substantially in contact with the outer side of the dielectric element and is preferably configured as a layer applied through a drying or curing liquid or suspension or is applied through a transition from a vapor phase into a solid phase.
15. The ionizing device according to claim 9, wherein the flow-through area of the outlet of the ionizing device is smaller than or equal to the area of the inlet of the ionizing device, and the outlet of the ionizing device has preferably arranged thereon a flow limitation unit.
16. The ionizing device according to claim 9, wherein a pressure gradient inside the ionizing device causes a flow with the flow direction in the ionizing device, preferably through a vacuum at the outlet and an essentially atmospheric pressure directly outside the inlet.
17. An analyzer for analyzing a sample substance in a discharge gas, comprising the ionizing device according to claim 9 and an analysis unit, the analysis unit being connected to the ionizing device.
18. The analyzer according to claim 17, wherein, in addition to the ionizing device, at least one further ionizing device is arranged.
19. The analyzer according to claim 17, wherein the inlet of the ionizing device is open to the surroundings and the discharge gas is preferably the atmosphere surrounding the inlet.
20. The method according to claim 1, wherein the applied voltage is not higher than 20 kV, preferably not higher than 10 kV, more preferably not higher than 5 kV and most preferably a voltage between 1 kV and 3 kV.
21. The method according to claim 1, wherein the dielectric barrier discharge is caused by unipolar high-voltage pulses having preferably a pulse duration of not more than 1 s, particularly preferred not more than 500 ns, and most preferred a duration between 100 ns and 350 ns.
22. The method according to claim 21, wherein the high-voltage pulses have a frequency that is not higher than 1 MHz, preferably not higher than 100 kHz, more preferably not higher than 25 kHz and most preferably a frequency between 1 kHz and 15 kHz.
23. The method according to claim 1, wherein the first and second electrodes are supplied with a sine-wave voltage, the sine-wave voltages of one electrode being preferably shifted by half a period relative to the other electrode.
24. The method according to claim 1, wherein the discharge gas flows through the ionizing device and the ionized discharge gas flows to the sample substance outside the ionizing device, the sample substance and the ionized discharge gas being jointly suppliable to an analyzer.
Description
(1) The embodiments of the present invention are illustrated by means of examples and not in a manner in which restrictions from the figures are transferred to or read into the claims.
(2) FIG. 1 shows an embodiment of an ionizing device 100 in a section through the longitudinal axis in the flow direction R.
(3) FIG. 1a shows an embodiment of an ionizing device 100 in a section through the longitudinal axis in the flow direction R with a positive value of the distance D.
(4) FIG. 1b shows an embodiment of an ionizing device 100 in a section through the longitudinal axis in the flow direction R with a negative value of the distance D.
(5) FIG. 1c shows an embodiment of an ionizing device 100 in a section through the longitudinal axis in the flow direction R with a value of the distance D equal to zero.
(6) FIG. 2 shows an embodiment of an ionizing device 100 in a section through the longitudinal axis in the flow direction R with a section perpendicular to the flow direction A-A.
(7) FIG. 3 shows an embodiment of an ionizing device 100 in a section through the longitudinal axis in the flow direction R with a flow limitation unit 20.
(8) FIG. 4 shows an embodiment of an ionizing device 100 in a section through the longitudinal axis in the flow direction R with a flow limitation unit and an inlet or an outlet A30.
(9) FIG. 5 shows an embodiment of an ionizing device 100 in a section A-A of the embodiment according to FIG. 2 perpendicular to the flow direction R.
(10) FIG. 6 shows an embodiment of an ionizing device 100 in a section perpendicular to the flow direction R.
(11) FIG. 7 shows an embodiment of an ionizing device 100 in a section perpendicular to the flow direction R.
(12) FIG. 8 shows an embodiment of an ionizing device 100 in a section perpendicular to the flow direction R.
(13) FIG. 9 shows an embodiment of an ionizing device 100 in a section perpendicular to the flow direction R.
(14) FIG. 10 shows an embodiment of an ionizing device 100 in a section perpendicular to the flow direction R.
(15) FIG. 11 shows an embodiment of an analyzer 200 in a section through the longitudinal axis in the flow direction R with an ionizing device 100 and an analysis unit 30.
(16) FIG. 1 shows an embodiment of an ionizing device 100 comprising a first electrode 1 that is in contact with the outer side 2a of a dielectric element 2. A second electrode 3 is arranged is partially inside the dielectric element 2 and is in contact with the inner side 2b of the dielectric element. In the present embodiment, the first and second electrodes 1, 3 and the dielectric element 2 are configured as cylindrical hollow bodies with open end faces. The outer diameter and the wall thickness of the first electrode 1 are selected such that the first electrode 1 is in contact with the dielectric element 2 and the outer diameter of the second electrode 3 is reduced in size relative to the first electrode 1 substantially by twice the wall thickness of the first electrode 1 and twice the wall thickness of the dielectric element 2. The ionizing device 100 allows a discharge gas G or a sample substance S (or a mixture of the discharge gas G and a sample substance S) to flow therethrough in a flow direction R. The discharge gas G and/or the sample substance S can enter the ionizing device 100 through the inlet E of the ionizing device 100, the inlet E being open to the surrounding atmosphere. In the present embodiment, the inlet E is defined as an area having the inner diameter of the second electrode by the open flow-through end face (contrary to the flow direction R) of the second electrode 3. According to other embodiments, the second electrode 3 may be arranged fully inside the dielectric element 2, so that the inlet E of the ionizing device 100 is defined by the open end face of the dielectric element 2, which is located in a direction opposite to the flow direction R. An outlet A of the ionizing device 100 is formed by the end face of the dielectric element 2 located in the flow direction R. The flow-through area of outlet A is determined by the inner diameter of the dielectric element 2. The first and second electrodes 1, 3 are arranged relative to one another in such a way that there is substantially no distance between them in the flow direction R. A distance of the electrodes 1, 3 perpendicular to the flow direction R results from the wall thickness of the dielectric element 2 located between the electrodes 1, 3.
(17) At the outlet A of the ionizing device 100, a vacuum unit 10 is arranged, in which a pressure below atmospheric pressure prevails, whereby a flow is caused in the ionizing device 100 and the pressure in the ionizing device 100 is controlled (by controlling the pressure in the vacuum unit 10). A vacuum unit 10 may be arranged on all embodiments of the ionizing device 100.
(18) When a voltage, especially an AC voltage, is applied to one or both of the electrodes 1, 3, a dielectric barrier discharge can occur in a dielectric barrier discharge region 110 so as to ionize a discharge gas G or the sample substance S. The dielectric barrier discharge range 110 is only schematically shown in FIG. 1 and indicates that the formation of a reactive species through the dielectric barrier discharge primarily takes place in the area between the electrodes 1, 3.
(19) According to another embodiment, the first and/or second electrode(s) 1, 3 may be positioned in the dielectric element 2 in such a way that the electrodes 1, 3 are insulated from each other.
(20) The distance D between the associated ends of the electrodes 1, 3 can be seen best in FIGS. 1a, 1b and 1c.
(21) In FIG. 1a, the distance D has a positive value (e.g. 1 mm) and results as a distance in or against the flow direction R between the two ends of the electrodes 1, 3. The end of the first electrode 1 defining the first end in the flow direction R and the end of the second electrode 3 defining the last end in the flow direction R are associated. In the case of positive values of the distance D, the electrodes 1, 3 do not overlap in or against the flow direction R.
(22) FIG. 1b shows a distance D of the associated ends of the first and second electrodes 1, 3 in or against the flow direction R with a negative value (for example 1 mm). If the electrodes 1, 3 overlap in or against the flow direction R, the end of the first electrode 1 defining the first end in the flow direction R is associated with the end of the second electrode 3 defining the last end in the flow direction R. If the electrodes 1, 3 overlap, negative values of the distance D will be obtained.
(23) In FIG. 1c, the distance D between the ends of the electrodes 1, 3 is zero. The end of the first electrode 1 defining the first end in the flow direction R and the end of the second electrode 3 defining the last end in the flow direction R are associated. The person skilled in the art will be able to see that such a borderline case should only exist within the framework of the measuring accuracy of a distance measurement.
(24) An arrangement of electrodes 1, 3 as in FIG. 1c provides the best results of ionization. With increasing distance D of the associated ends of the electrodes 1, 3, the efficiency of ionizing or ionization decreases, the decrease in efficiency with increasing magnitude of the negative values of the distance D being less substantial than the decrease in efficiency with increasing magnitude of positive values of the distance D.
(25) FIG. 2 shows an embodiment of an ionizing device 100 with overlapping electrodes 1, 3. The distance D has a negative value. A section A-A perpendicular to the direction of flow is introduced in order to show the cross-section more clearly (cf. FIG. 5).
(26) The outlet A of an ionizing device 100 has arranged thereon a flow limitation unit 20 in FIG. 3. An embodiment of the ionizing device according to FIG. 2 is exemplarily shown. A flow limitation unit 20 may also be arranged on any other embodiment of the ionizing device 100. In FIG. 3, the flow limitation unit 20 is configured as a reducer that is attachable to the ionizing device 100, whereby the flow-through area of the outlet A will be reduced. A flow through the ionizing device can be caused by a pressure gradient, for which a vacuum (established e.g. by a vacuum unit 10) is preferably applied to the outlet A of the ionizing device, the pressure prevailing outside the inlet being preferably atmospheric pressure. By reducing the cross-sectional area at the outlet A, the flow through the ionizing device 100 can easily be regulated at a given pressure gradient (e.g. by a specific vacuum at the outlet A20 of the flow limitation unit 20). When a flow limitation unit 20 and a predetermined vacuum at the outlet A20 of the flow limitation unit 20 are used, the pressure gradient in the ionizing device 100 will be low in comparison with a pressure gradient occurring without a flow limitation unit 20. Depending on the specific dimensions of the flow limitation unit 20 and of the ionizing device 100, the pressure in the dielectric barrier discharge region 110 will be significantly higher than the pressure at the outlet A20 of the flow limitation unit 20 and only slightly lower than atmospheric pressure, which preferably prevails outside the inlet E. To the person skilled in the art it will be understandable that the specific pressure conditions result from the structural design of the respective components, from material-specific characteristics and from the physical boundary conditions (temperature, ambient pressure, etc.). The absolute pressure in the dielectric barrier discharge region 110 is preferably higher than 40 kPa. The flow rate through the ionizing device 100 is preferably between 0.01 L/min and 10 L/min and particularly preferred between 0.1 L/min and 1.5 L/min.
(27) Flow regulation by means of a reduction of the cross-sectional area can be effected not only by a flow limitation unit 20 but also by other measures taken with respect to the structural design or control technology (e.g. through a controllable change in cross-section by means of a valve or through a variable vacuum). For example, a narrowing of the outlet A of the ionizing device 100 by means of a non-constant cross-section of the dielectric element 2 may be advantageous. Other suitable measures for regulating the pressure in the ionizing device 100 and/or the flow through the ionizing device may, however, be taken.
(28) FIG. 4 shows a further embodiment of an ionizing device 100 with an inlet or outlet A30. The inlet or outlet A30 is combinable in all other embodiments of an ionizing device 100 according to the present invention (with or without a flow limitation unit 20). The inlet or outlet A30 is configured such that, in the flow direction R downstream or upstream of the dielectric barrier discharge region 110, an additional substance can be introduced into the ionizing device 100 or part of the flowing discharge gas G and of the sample substance S can be discharged.
(29) FIG. 5 shows a section A-A perpendicular to the flow direction R through the part of the embodiment of an ionizing device 100 of FIG. 2 in which the electrodes 1, 3 overlap. The first electrode 1, the dielectric element 2 and the second electrode 3 have a circular cross-section. The first electrode 1 is in contact with the outer side 2a of the dielectric element 2, the second electrode 3 is in contact with the inner side 2b of the dielectric element 2. According to another embodiment, the second electrode 3 is not in contact with the inner side 2b of the dielectric element 2 and a discharge gas G and a sample substance S flowing through the ionizing device 100 may flow through and around the second electrode 3.
(30) In FIG. 6, the second electrode 3 is configured as a wire or an elongated body arranged in the central area (area perpendicular to the flow direction R) of an ionizing device 100. The inner side 2b of the dielectric element 2 may be contacted by a discharge gas G and a sample substance S flowing through the ionizing device 100. The first electrode 1 is in contact with the outer side 2a of the dielectric element 2.
(31) In FIG. 7, the second electrode 3 is configured as a wire or an elongated body. The inner side 2b of the dielectric element 2 is in contact with the second electrode 3. A discharge gas G and a sample substance S can flow through the annular gap that forms between the dielectric element 2 and the first electrode 1.
(32) In addition to the embodiment shown in FIG. 6, a body K is arranged around the first electrode 1 in the embodiment of the ionizing device 100 shown in FIG. 8. The second electrode 3 is configured as a wire or an elongated body and does not contact the inner side 2b of the dielectric element 2. The first electrode 1 is in contact with the outer side 2a of the dielectric element 2. The body K surrounds the first electrode 1 in such a way that a discharge gas G and a sample substance S flowing through the ionizing device 100 can be divided into two flowing parts. A first part can flow through an annular gap formed between the body K and the first electrode 1 and a second part can flow through an annular gap formed between the second electrode 3 and the dielectric element 2. The discharge gas G and the sample substance S are preferably ionizable exclusively or mainly in the annular gap between the second electrode 3 and the dielectric element 2. The dielectric barrier discharge region 110 preferably extends mainly only into the annular gap between the second electrode 3 and the dielectric element 2. The flow of the discharge gas G and of the sample substance S, which can be divided in the case of the present embodiment, is preferably dividable into the first and second parts downstream of the inlet E into the ionizing device 100 and combinable upstream (in each case seen in the flow direction R) of the outlet A of the ionizing device 100. This kind of structural design offers the possibility of ionizing only a certain part (depending on the specific dimensions of the components of the present embodiment of the ionizing device 100) of the discharge gas G and of the sample substance S, thus also reducing a minor fragmentation of ionized substances, since the part of the substances that does not flow through the dielectric barrier discharge region comes into contact with the part of the substances that has flown through the dielectric barrier discharge region during mixing of these parts, and it can be ionized e.g. by charge transfer reactions.
(33) An embodiment of the ionizing device 100 in FIG. 9 comprises a first electrode 1, a dielectric element 2 and a second electrode 3, which have a rectangular basic shape. The second electrode 3 is surrounded by the sides of the dielectric element 2 (inner side 2b) and a discharge gas G as well as a sample substance S can flow therethrough and therearound. The first electrode 1 is in contact with the outer side 2a of the dielectric element 2.
(34) The first electrode 1, the dielectric element 2 and the second electrode 3 of the embodiment of the ionizing device 100 shown in FIG. 10 have a triangular basic shape and are otherwise configured analogously to the embodiment of FIG. 9. In the case of basic geometric shapes having more than one side (for example triangles, other polygonal shapes or other basic shapes), internal sides are summarized as an inner side and external sides as an outer side.
(35) In other embodiments, various polygonal, elliptical and other basic shapes may be advantageous.
(36) All the cross-sections of FIGS. 5 to 10 may be cross-sections of the various embodiments of the ionizing device 100 disclosed here.
(37) An analyzer 200 shown in FIG. 11 comprises an arbitrary embodiment of the ionizing device 100, which is connected to an analysis unit 30. The connection between the ionizing device 100 and the analysis unit 30 may be configured in different ways. For example, a direct connection (the ionizing device 100 merges directly with the analysis unit 30) may be formed, or an intermediate or transition piece may be arranged between the ionizing device 100 and the analysis unit 30. When a discharge gas G and a sample substance S flow through the ionizing device 100, the discharge gas G and the sample substance S can be ionized. When the ionized discharge gas G and the ionized sample substance S enter the analysis unit 30, the ionized sample substance S can be analyzed. In principle, any analysis unit that is capable of analyzing a property of a charged sample substance is suitable for use as an analysis unit 30. An analysis unit 30 may e.g. be a mass spectrometer, an ion mobility spectrometer or some other unit known as such. Also an analyzer 200 may have attached thereto a vacuum unit 10.
