EP1220285B1 - Ion source in which a UV/VUV light source is used for ionization - Google Patents

Description

The invention relates to an ion source for selective one-photon ionization of an analysis gas according to the preamble of patent claim 1, as well as their use.

VUV - light can be generated by so-called micro hollow cathode lamps. In this case one or more parallel burning discharges into small (typically 100 μ _m Druchmesser) openings are constricted in a dielectric. Since gas discharge parameters scale with the product of diameter and gas pressure, the arrangement, in turn, can maintain a stable glow discharge because of the small diameter with high gas pressure and generate VUV excimer light in the dense gas [1].

Another alternative variant for generating brilliant UV / VUV radiation is a discharge in dense noble gases between pointed metal electrodes or a tip metal electrode and a metal surface. These variances of the corona discharge are operated both with high frequency and with direct voltage [ DE Murnick, M.Salvermoser, priv. Communication, Gaseous Electronics Conference "GEC" 2000, 24.-27. October, Houston, Texas, USA, accepted for publication s].

A particularly suitable for ion sources UV / VUV light source is the electron beam pumped structure described below.

The vacuum ultraviolet light generation in the light source, which generates the ions in the ion source by photoionization, is effected by the excitation of a dense gas with an electron beam [2, 3]. The gas usually consists of one of the noble gases He, Ne, Ar, Kr or Xe or a noble gas and the admixture of another gas, such as hydrogen.

State of the art

Mass spectrometry using laser-based VUV single-photon ionization where the VUV light from UV laser pulses by frequency tripling in a gas cell, and their use for chemical analysis is described in the literature [5-8]. However, the laser-based generation of VUV Licht has some serious disadvantages.

The VUV generation process in a gas cell is very inefficient. Therefore, powerful and therefore very expensive, large solid-state lasers must be used (usually Nd: YAG laser with 355 nm). In operation, high incidental costs arise due to flash lamps (required for pumping the laser medium) and maintenance. Furthermore, with a solid-state laser in general, only a single VUV wavelength can be generated (118 nm using 355 nm laser radiation). Tunable solid-state lasers are extremely expensive and can not be used for practical analytical tasks. Frequency tripling is a very sensitive nonlinear process whose VUV yield scales with the cube of the primary radiation. This leads to a high instability of the system and to fluctuations in the VUV yield. Furthermore, a complex separation of the primary radiation 355 nm is necessary to prevent fragmentation of the ions formed by VUV absorption.

In addition to laser-based VUV single-photon ionization, the use of conventional low-pressure emission lamps (for example mercury vapor lamps) for ion generation for mass spectrometry is also possible in principle.

In addition, deuterium lamps based on a gas discharge in a deuterium gas and when used with a vacuum ultraviolet light transmissive window, e.g. B consisting of MgF ₂ or LiF, continuum radiation and the so-called Lyman and Werner molecular bands to emit 160 or 130 nm. Deuterium lamps are commercially available from various manufacturers.

Furthermore, VUV light can be generated with so-called dielectrically impeded discharges, wherein in the case of a gas discharge at least one of the electrodes is provided with a non-conductive layer. [9]. In this arrangement, for example, in dense, cold noble gases by applying a medium-frequency AC voltage to the electrodes excimer light in the VUV range can be generated.

However, these lamps produce a wide range of wavelengths (requires wavelength separation and low useable photon density) and are not very brilliant (this causes, for example, poor focusability).
BOBELDIJK M ET AL: "TESTING THE PERFORMANCE OF A VUV PHOTOIONIZATION SOURCE ON A DOUBLE FOCUSSING MASS SPECTROMETER USING ALKANES AND THIOPHENES", INTERNATIONAL JOURNAL OF MASS SPECTROMETRY AND ION PROCESSES, ELSEVIER SCIENTIFIC PUBLISHING CO. AMSTERDAM, NL, Vol. 110, No. 3, 2 December 1991 (1991-12-02), pages 179-194 and GENUIT W. ET AL .: "SELECTIVE ION SOURCE FOR TRACE GAS ANALSIS", INTERNATIONAL JOURNAL OF MASS SPECTROMETRY AND ION PHYSICS, Vol. 51, 1983, pages 207-213 disclose an ion source for selective one-ion ionization of an analysis gas, having an ionization space for receiving the analysis gas and a UV / VUV excimer glow discharge lamp for generating ions from the analysis gas in the ionization space by UV / VUV.
US 6 052 401 A . WIESER J ET AL: "VACUUM ULTRAVIOLET RARE GAS EXCIMER LIGHT SOURCE", REVIEW OF SCIENTIFIC INSTRUMENTS, AMERICAN INSTITUTE OF PHYSICS. NEW YORK, US, Vol. 68, No. 3, March 1997 (1997-03), pages 1360-1364 , and SALVERMOSER M ET AL: "Energy flow and excimer yields in continuous wave rare gas-halogen systems", JOURNAL OF APPLIED PHYSICS, AMERICAN INSTITUTE OF PHYSICS. NEW YORK, US, Vol. 88, No. 1, July 1, 2000 (2000-07-01), pages 453-459 disclose an electron beam driven UV / VUV excimer lamp.
EP 0 585 487 A discloses a device for photoionization of trace elements in a carrier gas and a corresponding detection. The light source is a flashlamp or a laser.

Task and examples

The object of the invention is to provide an ion source with a light source of high useful photon density and to provide an advantageous use This object is achieved by the features of claims 1 and 6. The dependent claims describe advantageous embodiments of the invention.

• Figur 1
  Ionisationsraum eines Flugzeitmassenspektrometers mit elektronenstrahlgepumpter Excimer VUV-Lampe.
• Figur 2
  Detaildarstellung eines Teils der Excimer-VUV-Lampe mit einem Parabolspiegel zur Zusammenfassung des UV/VUV-Lichtes.
• Figur 3
  Übersichtsdarstellung des Flugzeitmassenspektrometers (TOFMS) mit Excimer-VUV-Lampen-Ionisation.
• Figur 4
  Optische Aufbauten zur Einkopplung des UV/VUV-Lichtes in die Ionisationsregion des Flugzeitmassenspektrometers (TOFMS).
• Figur 5
  Gemessene Zeitabläufe während eines Nachweiszyklus mit einem Excimer-VUV-Lampen-Ionisations Flugzeitmassenspektrometer (Prototyp). Dargestellt sind der VUV-Lichtimpuls (Kr), Abzugspannungsimpuls und das Ionendetektorsignal.
• Figur 6
  Wellenlängenselektivität der Massenspektrometrie mit Excimer-VUV-Lampen-Ionisation. Dargestellt ist das Wellenlängenspektrum der Argon bzw. Krypton Excimer-Emission sowie die korrespondierenden Excimer-VUV-Lampen-Ionisation Flugzeitmassenspektren einer Mischung aus Benzol und Toluol.
• Figur 7
  Mit einem Excimer-VUV-Lampen-Ionisations Flugzeitmassenspektrometer (Prototyp) durchgeführte on-line Messung von Abgas eines Motorrads während der Startphase (Excimergas: Argon)
• Figur 8
  Schematische Übersichtsdarstellung des Quadrupol-Massenspektrometers (QMS) mit Excimer-VUV-Lampen-Ionisation.
• Figur 9
  Schematische Übersichtsdarstellung eines Detektors für Gase auf Basis einer Ionisationskammer mit Excimer-VUV-Lampen-Ionisation und Detektion der erzeugten Ladungen.
• Figur 10
  Schematische Übersichtsdarstellung einer VUV-Lampe, bei der durch Ablenkung des Elektronenstrahls auf verschiedene Eximer-VUV-Lichtquellen mit unterschiedlicher Gasfüllung die Wellenlänge des emittierten Lichts verändert werden kann.

In the following the invention will be explained in more detail by means of exemplary embodiments and the figures. Showing:

• FIG. 1
  Ionization chamber of a time-of-flight mass spectrometer with electron beam-pumped excimer VUV lamp.
• FIG. 2
  Detail view of a part of the excimer VUV lamp with a parabolic mirror to summarize the UV / VUV light.
• FIG. 3
  Overview of Time of Flight Mass Spectrometer (TOFMS) with Excimer VUV Lamp Ionization.
• FIG. 4
  Optical structures for coupling the UV / VUV light into the ionization region of the time-of-flight mass spectrometer (TOFMS).
• FIG. 5
  Measured timings during a detection cycle with an excimer VUV lamp ionization time-of-flight mass spectrometer (prototype). Shown are the VUV light pulse (Kr), pull-off voltage pulse and the ion detector signal.
• FIG. 6
  Wavelength selectivity of mass spectrometry with excimer VUV lamp ionization. Shown is the wavelength spectrum of the argon or krypton excimer emission and the corresponding excimer VUV lamp ionization time-of-flight mass spectra of a mixture of benzene and toluene.
• FIG. 7
  Using an excimer VUV lamp ionization time-of-flight mass spectrometer (prototype) on-line measurement of exhaust gas of a motorcycle during start-up (excimer gas: argon)
• FIG. 8
  Schematic overview of the quadrupole mass spectrometer (QMS) with excimer VUV lamp ionization.
• FIG. 9
  Schematic overview of a detector for gases based on an ionization chamber with excimer VUV lamp ionization and detection of the generated charges.
• FIG. 10
  Schematic overview of a VUV lamp in which the wavelength of the emitted light can be changed by deflecting the electron beam to different Eximer VUV light sources with different gas filling.

UV / VUV excimer lamp

The FIG. 1 shows by way of example the configuration of the ionization region of a time-of-flight mass spectrometer with VUV eximer lamp ionization. The FIG. 2 shows a section of the beam injection and FIG. 3 the entire mass spectrometer with the VUV eximer lamp. The FIG. 4 shows different possibilities for coupling the UV / VUV light into the ionization chamber 14 or to the ionization site 23. Die Figures 5 and 6 show exemplary application results with the developed prototype.

The VUV Eximerlampeneinheit is coupled for example via a flange to the ionization chamber 14. The upper part of the lamp is used to generate an electron beam 8 with the electron gun 1 and has a vacuum. The electron tube 2 is evacuated via a getter pump 4 and a pump nozzle 5. The electron beam 8 is focused on the film 3. The film consists for example of ceramic silicon nitride and separates the high vacuum of the electron tube 2 from the gas space 9. In the gas space 9 there is a gas mixture which lights up via the electron-beam-pumped excimer process in the UV / VUV spectral range (radiative decay of the excimers). The gas space 9 is cleaned via a getter 10. In the gas space 9 there is a suitably coated parabolic mirror 11, which combines the UV / VUV light formed in the luminescence volume 13 into a parallel beam and throws it onto the lens 12. This construction allows a good utilization of the 360 degree radiation space angle. A reflective coating of the side of the film 3 directed toward the gas space 9 can further improve the yield of the useful UV / VU radiation. The lens 12 is made of UV / VUV transparent material (eg, MgF 2 or LiF) and separates the gas space 9 from the ionization space 14 of the time-of-flight mass spectrometer (TOFMS). The lens (12) focuses the UV / VUV light on the ionization site 23. When using a needle inlet 15, the ionization site 23 is located behind the inlet needle 15 (in FIG molecular beam formed from the analysis gas) between the electrodes 18 and 16 of the TOFMS.

As an alternative to the lens 12, a multimicro channel light guide 24 or 25 can be used. A multimicro channel light guide 24 consists of a bundle with a large number of narrow capillaries (analogous to a microchannel plate). The UV / VUV light passing through the capillaries may enter the ionization space 14 which has a vacuum. If the capillaries are sufficiently long and thin, the gas flow from the gas space 9 through the multi-microchannel light guide 24 into the ionization space 14 is very low (ie the vacuum in 14 is not overburdened). The UV / VUV light falls either directly through the clear width of the capillary or is passed through one or more total reflections through the capillaries of the multimicro channel light guide 24. Furthermore, a multi-microchannel light guide 25 can be used, which allows a focusing of the transmitted UV / VUV light beam 22 to the ionization 23 by a conical taper of the capillary bundles. The main advantage of using multichannel light guides 24 or 25 is that they can transmit these VUV light with wavelengths smaller than 110 nm. Optical lenses 12 or windows for decoupling can be used only up to about this wavelength due to the incipient intrinsic absorption of the material (LiF, MgF ₂ ).

In the example presented, the entire optical system for coupling the UV / VUV radiation into the ionization chamber 14 consists of the parabolic mirror 11 and the lens 12 or a multimicro channel light guide 24 or 25. Furthermore, a combination of a lens 12 or a multimicro channel light guide 25 with a hollow optical waveguide is also possible 26, which leads the UV / VUV light via total reflections directly to the ionization 25, possible.

It is important in the design of the coupling of the UV / VUV radiation in the ionization chamber 14 that a high beam density is reached at the ionization 23.

Im in FIGS. 1 As shown, the inlet of the analysis gas into the mass spectrometer takes place effusively via an inlet needle 15 [10]. Other sample gas inlet techniques, such as pulsed [11] or continuous supersonic molecular beams [12], can also be used.

The FIG. 3 shows a schematic representation of a time-of-flight mass spectrometer (TOFMS, without depiction of the vacuum pumps, the reflectron ion mirror and other details) with electron-beam-pumped excimer lamp ionization. The UV / VUV light from the electron beam pumped excimer lamp 20 is focused through the optical elements described above into the effusive molecular beam emerging from the inlet needle 15. The voltages in the ion source (simplified here with the Elektoden18,16 and 17 shown) are chosen so that the ionization space is field-free. The ions formed by single-photon absorption of VUV photons are therefore not influenced by electric fields. Thus, the ions formed accumulate at and around the ionization site 23. This ion accumulation can be operated for about several μs, after which the ions again leave the acceptance volume of the time-of-flight mass spectrometer (ie the volume that can be imaged on the ion detector 21) due to space charge effects and the intrinsic velocity of the particles from the effusive molecular beam. In order to detect the enriched ions, abruptly suitable potentials are applied to the electrodes 18, 16 and 17 via the controlled, pulsable high-voltage supply 19. The rising edges of the voltage pulses are usually in the range of a few ns. The ions are accelerated to the detector 21. In the field-free drift space (space between aperture 17 and detector 21), the ions separate according to their mass. The time-of-flight mass spectrum is registered at the detector 21 with suitable electronics (not shown). The panels 16 and 17 may consist of pinholes with or without networks or even networks. The mass resolution and sensitivity in the above-described operation of the TOFMS with ionization by continuous radiating VUV excimer lamps is limited, since due to the continuous operation of the lamp new ions are formed during the extraction of ions. These "post-formed" ions reach the detector later than ions of equal mass formed during the enrichment time (ie, peak spreads and increased background signal occur).

The above-described disadvantages of the continuous operation of the VUV excimer lamp can be avoided by the pulsed operation of the VUV excimer lamp.

In this case, the electron beam 8 is directed in a pulsed manner (for example by pulsed diaphragms in the electron gun or by deflection plates) onto the foil 3. In a pulsed operation of the lamp 20, the electron density can be increased without thermally overloading the film 3. When the electron beam 8 is turned off, the VUV light emission 22 collapses within 500 to 1000 ns. This can be exploited to extract the ions from the ion source at already significantly reduced VUV light intensity. The FIG. 5 shows measured parameters of VUV excimer lamp ionization TOFMS (prototype) in pulsed mode. The upper trace shows the light pulse of the excimer lamp measured with a photodetector. The middle track shows the trigger pulse of the ion source and the bottom track shows the ion detector signal. Piperidine (85 m / z) and toluene (92 m / z) were admixed, the corresponding mass peaks being visible in the lower lane.

An important advantage of the VUV excimer lamp ionization is that 9 different wavelengths can be set by the choice of the gas in the gas space.

The selectivity of one-photon ionization is due to the fact that only molecules can be ionized whose ionization energy is below the photon energy of the irradiated VUV light lies. This allows the suppression of ionization of compounds such as oxygen, nitrogen or noble gases, which have very high ionization energies. Therefore, VUV ionization is very well suited for on-line analysis of trace compounds from air or process gases (exhaust gases) since the main components of the gas mixture are not ionized. Furthermore, by using different wavelengths, a more accurate statement about the composition of the observed peaks in the mass spectrum can be obtained. For example, at photon energies of about 9 eV, participation of aliphatic organic compounds in the mass spectrum can be ruled out. In Table 1, various gases or gas mixtures with the corresponding emission wavelengths (maximum values) are given. The FIG. 6 shows the emission profiles of the VUV excimer lamp for argon (left, top) and krypton (left, bottom). Also marked are the ionization energies of benzene and toluene. On the right side, the associated measured TOFMS mass spectra of a mixture of benzene (92 m / z) and toluene are shown. The argon excimer emission (top) is 128 nm (9.7 eV). Both benzene and toluene are therefore efficiently ionized. The krypton excimer emission (below) is 150 nm (8.2 eV). Here, toluene lies directly in the center of the emission curve, whereas benzene is only detected by a "shoulder emission" on the high-energy side. In the mass spectrum, therefore, the toluene peak is orders of magnitude more intense than the benzene peak.

Due to the relatively broad emission spectra ( FIG. 6 , left) the selectivity is only mediocre. With monochromatic radiation, a higher selectivity could be achieved. This can be achieved in several ways. By adding certain gases, the emission can be transferred to a narrow-band emission line. For example, a narrow band emission of 121.57 nm can be achieved with a mixture of hydrogen and neon (see Table 1). Alternatively, a narrow region can be cut out of the broadband emission spectrum. This is z. B. by filter / mirror with dichroic coating (interference filter) possible. The FIG. 7 shows a first application measurement with the developed prototype of a time-of-flight mass spectrometer with VUV excimer lamp ionization. Exhaust gas from a motorcycle (TYP 43F) was introduced into the mass spectrum via the inlet needle 15 via an on-line sampling system. The lamp was operated with argon (128 nm). The figure shows a 3D plot of mass spectrometric information (mass, time, intensity) taken during a motorcycle launch. Various aromatic compounds (benzene and methylated benzenes) exhibit a highly dynamic, fluctuating time course due to transient combustion conditions during the startup phase of the engine. Mass spectrometers with VUV excimer lamp ionization can advantageously be used for fast time-resolved on-line analysis of process gases or for headspace analysis. Possible fields of application are, for example, in the area of the food industry (monitoring of roasting, baking, cooking or ripening etc.) of the chemical industry (monitoring of syntheses, waste streams, mineral oil processing, etc.), monitoring of combustion processes and other production processes.

2) Quadrupole mass spectrometer with electron beam pumped UV / VUV excimer lamp

The VUV excimer lamp ionization can also be used with other non-pulsed mass spectrometer types such as the TOFMS. The FIG. 8 shows a constructed according to the invention VUV excimer lamp with optical elements for focusing the VUV light on the ionization region of a quadrupole mass spectrometer. Here, the VUV excimer lamp 20 is advantageously operated continuously. The ion source 29 generates a continuous ion beam. The alternating electric fields applied to the quadrupole rods 27 (generated by the controller 28) allow only ions of a mass to pass from the ion beam to the detector 30. By changing the alternating fields by means of the controller 28, the quadrupole mass spectrometer can be successively set to a transmission set different masses and so a Massesnspektrum can be recorded. Possible fields of application of quadrupole mass spectrometry with VUV excimer lamps Ionisation is in the area of the food industry (monitoring of roast, baking, cooking or maturing etc.) of the chemical industry (monitoring of syntheses, waste streams, mineral oil processing, etc.), during monitoring combustion processes and other production processes.

3) E-beam pumped excimer lamp ionization for mass spectrometry in gas chromatography-mass spectrometry (GC-MS) coupling

GC-MS is a standard technique of organic trace analysis. The use of VUV light for ionization for mass spectrometry in a gas chromatography-mass spectrometry coupling brings another level of selectivity to mass spectrometry. Certain compounds with higher ionization energies can be excluded from ionization. In addition, a fragment-free ionization compared to the standard technique of electron impact ionization (EI) is achieved. Various mass spectrometer types (ion trap MS, sector field MS, Qudrupol MS, time of flight MS) can be used for this purpose.

4) Electron beam pumped UV / VUV excimer lamp for ionization cell detectors

To determine whether organic compounds (and / or inorganic compounds with a low ionization threshold) are present in an air sample, it is not absolutely necessary to use a mass spectrometer. It is sufficient to generate ions and electrons in an ionization space by irradiation of the VUV light and to detect these, for example, via the charge flow by means of an ammeter 34 or at a resistor by means of an oscilloscope. The FIG. 9 shows the schematic structure of an ionization cell detector with the VUV excimer lamp 20 of the generic type. In the ionization cell (ie the Ionisationsraum 14) are the electrodes 31 and 32. Between the electrodes 31 and 32, a suitable pull-off voltage is applied via a voltage supply 33. The sample gas passes through an inlet 15 between the electrodes 31 and 32 to the ionization zone. For example, via an ammeter 34, the photocurrent (Photoionenstrom and photoelectron current) can be detected.

Such a detector has approximately the properties of a flame ionization detector, so it responds to most organic compounds and to some inorganic species. Due to the different wavelengths that can be provided with different gas fillings / optical systems, some selectivity can be achieved. A VUV excimer lamp ionization cell detector can thus be used advantageously for various applications. For example, it can be used as a detector for gas chromatography. Another possible application is the use as a sensor for the occurrence of organic compounds in gas mixtures.

5) Multi-lamp assembly with an electron gun for MS and meters

FIG. 10 shows by way of example the structure of an excimer VUV lamp in which by means of an electron gun 1 one of the two excimer light sources 36 of the generic type depending on the applied electric field between the deflection electrodes 35 is pumped and thus brought to light. If the gas spaces 9 of the two excimer light sources are filled with different gases or gas mixtures (see Table 1), the photons of the generated light of the two excimer light sources have a different photon energy.

Due to the ionization potential, substances in the mass spectrum can thus be faded in or out in the analysis of a complex sample gas by means of a light beam from one or the other light source. Likewise, by appropriate choice of the Gas or gas mixture and thus the photon energy isobaric compounds are detected separately.

LIST OF REFERENCE NUMBERS

1

electron gun

2

Space of the electron gun (vacuum)

3

Membrane (eg 1x1 mm ² , thickness = 300 nm made of SiNx ceramic)

4

Getter pump

5

Valve for pumping

6

gas inlet

7

gas outlet

8th

electron beam

9

Gas space (e.g., filled with 500 mbar argon)

10

Getter cartridge

11

Reflector (eg aluminum parabolic mirror with MgF ₂ coating)

12

Lens (eg made of MgF ₂ )

13

UV / VUV light emitting gas volume

14

ionization chamber

15

Gas inlet needle

16

first withdrawal electrode

17

second extraction electrode

18

Repeller electrode

19

Pulsable power supply for the electrodes 16,17 and 18 and control

20

entire UV / VUV light source

21

detector

22

UV / VUV beam

23

ionization

24

non-focusing multimicro channel light guide

25

focusing multimicro channel light guide

26

Hollow fiber

27

Quardrupolstäbe

28

Control of the Quardrupolionenfilters

29

continuous ion source for the quadrupole mass spectrometer

30

ion detector

31

Electrode of the measuring capacitor (positive voltage, photon trap)

32

Electrode of the measuring capacitor (negative voltage, photoio-catcher)

33

power supply

34

electrometer

35

deflection

36

UV / VUV light source

table

Table 1 Gas or gas mixture Animated species wavelength bandwidth He Hey ₂ * 60 nm / 80 nm ne Ne ₂ * 83 nm broadband Ar Ar ₂ * 128 nm broadband Kr Kr ₂ * 150 nm broadband Xe Xe ₂ * 172 nm broadband Ne / H ₂ H* 121.57 nm narrow band Ar / Xe Kr / Xe Xe * 147 nm narrow band Ar / O ₂ O* 130 nm narrow band Ne / Ar / Kr Kr * 124 nm narrow band Ar / F ₂ Ne / F ₂ F ₂ * 157 nm narrow band Ar / F ₂ ArF * 193 nm narrow band

Bibliography:

• [1] El-Habachi, A., K. Schoenbach; Appl. Phys. Lett. 72, 22 (1998 )
• [2] Wieser, J., DE Murnick, A. Ulrich, HA Huggins, A. Liddle, WL Brown; Rev. Sci. Instrum. 68 (3), 1360-1364 (1997 )
• [3] Salvermoser, M., DE Murnick; Journal of Applied Physics 88 (1), 453-459 (2000 )
• [4] Wieser, J., Salvermoser, LH Shaw, A. Ulrich, DE Murick, H. Dahi; 31, 4589-4597 (1998)
• [5] Butcher, DJ, DE Goeringer, GB Hurst; Anal. Chem. 71 (2), 489-496 (1999 )
• [6] Becker, CH; Fresen. J. Anal. Chem. 341, 3-6 (1991 )
• [7] Van Bramer, SE, MV Johnston; J. Am. Soc. Mass Spectr. 1, 419-426 (1990 )
• [8th] Shi, YJ, XK Hu, DM Mao, SS Dimov, RH Lipson; Anal. Chem. 70, 4534-4539 (1998 )
• [9] Gellert, BB, U. Kogelschatz; Applied Physics B 52, 14 (1991 )
• [10] Heger, HJ, R. Zimmermann, R. Dorfner, M. Beckmann, H. Griebel, A. Kettrup, U. Boesl; Anal. Chem. 71, 46-57 (1999 )
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• [12] Fricke, J .; Phys. Our time 1, 21-27 (1973 )

Claims (10)

1. Ion source for selective single-ion ionisation of an analysis gas, comprising:

   an ionisation chamber (14) for accommodating the analysis gas; and

   an electron-ray-operated UV/VUV excimer lamp (20) for generating ions from the analysis gas in the ionisation chamber (14) by means of UV/VUV light, the electron-ray-operated UV/VUV excimer lamp having

   - an electron cannon (1) for generating an electron ray (8) ;

   - an electron tube (2) comprising the electron cannon (1) ;

   - a gas chamber (9) having a noble gas or a gas mixture containing noble gas in the gas chamber (9);

   - a membrane (3) for closing off the electron tube (2) from the gas chamber (9), through which membrane the electron ray (8) passes, the electron ray which passes through the membrane (3) generating UV/VUV light in the gas chamber (9);

   - a parabolic mirror (11) arranged in the gas chamber (9) for combining UV/VUV light formed in a luminescence volume (13) of the gas chamber (9) into a parallel beam; and

   - a lens (12) arranged in the gas chamber (9) or a multi-microchannel light guide (2, 5) arranged in the gas chamber (9) for focussing the parallel beam of UV/VUV light, formed by the parabolic mirror, onto an ionisation site (23) in the ionisation chamber (14).
2. Ion source according to claim 1, characterised by a Getter pump (4) in the chamber of the electron cannon (1).
3. Ion source according to either claim 1 or claim 2, characterised by a gas inlet and outlet (6, 7) at the gas chamber (9).
4. Ion source according to any one of claims 1 to 3, characterised by a Getter cartridge (1) which is connected to the gas chamber (9).
5. Ion source according to any one of claims 1 to 4, characterised by at least one electrode for pulsing the electron beam (8) of the electron cannon (1).
6. Use of the ion source according to any one of claims 1 to 5 for generating ions, in connection with the detection thereof in an ion detection device.
7. Use of the ion source according to claim 6, wherein the ion detection device is a mass spectrometer.
8. Use of the ion source according to claim 7, characterised in that a time-of-flight mass spectrometer (TOFMS) is used as the mass spectrometer.
9. Use of the ion source according to claim 7, characterised in that a quadrupole mass spectrometer is used as the mass spectrometer.
10. Use of the ion source according to claim 8, characterised in that the ionisation chamber is additionally irradiated with a laser so as to generate ions by a REMPI (resonance-enhanced multi-photon ionisation) process.

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