WO2020169967A1 - A gas cell for a photoionisation detector - Google Patents

A gas cell for a photoionisation detector Download PDF

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Publication number
WO2020169967A1
WO2020169967A1 PCT/GB2020/050393 GB2020050393W WO2020169967A1 WO 2020169967 A1 WO2020169967 A1 WO 2020169967A1 GB 2020050393 W GB2020050393 W GB 2020050393W WO 2020169967 A1 WO2020169967 A1 WO 2020169967A1
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Prior art keywords
gas cell
filter
photoionisation
enclosure
aperture
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PCT/GB2020/050393
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French (fr)
Inventor
Andrew David WITTY
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Ion Science Limited
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Publication of WO2020169967A1 publication Critical patent/WO2020169967A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/62—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode
    • G01N27/64—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode using wave or particle radiation to ionise a gas, e.g. in an ionisation chamber
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/0047—Organic compounds

Definitions

  • the invention relates to a gas cell for a photoionisation detector, in particular a gas cell for a photoionisation detector comprising an enclosure and an electrically isolated metal first filter for permitting, in use, diffusion controlled ingress of a gaseous analyte into the enclosure and a photoionisation detector comprising the said gas cell.
  • Photoionisation detection engages ultra-violet radiation, of typical photon energies in the range 8 to 12 eV, to collide with a gaseous analyte, typically a volatile organic compound (VOC), causing its fragmentation into electrons and photo-ions, in a process known as photoionisation.
  • a gaseous analyte typically a volatile organic compound (VOC)
  • VOC volatile organic compound
  • Photoionisation detectors photoionisation is usually confined by an enclosure which includes as one wall member one face of a crystal window through which the photoionising radiation is presented to the enclosure.
  • a detector typical comprises at least two electrodes located within the enclosure connected by an electric circuit.
  • an electric field is generated between the electrodes causing the generated electrons and photo-ions to separate according to their electric charge and migrate to one of the two electrodes where their electric charge is neutralised by transfer of electrons to or from the electrodes.
  • the resulting electric current which flows between the electrodes is amplified and output as a signal indicative of the concentration of photo-ions inside the enclosure.
  • the enclosure is only partial and is substantially open to a gaseous environment, the signal due to a gaseous analyte is prone to instability.
  • One reason for signal instability is that diffusion of the gaseous analyte near the open end of the enclosure is susceptible to natural air currents. It is therefore very typical for an enclosure to comprise a filter for permitting, in use, diffusion controlled ingress of the gaseous analyte into the enclosure.
  • the filter is typically formed from polytetrafluoroethylene (PTFE).
  • PTFE polytetrafluoroethylene
  • PTFE is an appropriate material because it is readily available, not readily photo-ionised and does not significantly adsorb gaseous analytes such as VOCs which might otherwise cause a retarded response to both a positively and a negatively changing gaseous analyte concentration within the enclosure.
  • PTFE is resilient to the corrosive gases commonly encountered in environments where photoionisation detectors are often deployed, highly electrically resistive therefore not interacting with the electric field in the enclosure, and has a low dielectric constant and therefore highly repellent to water which may be presented to the detector in the form of condensation or smoke particles.
  • a gas cell for a photon ionisation detector comprising an enclosure and at least one pair of cathode and anode electrodes at different electrical potentials for measuring a photoionisation current between the electrodes in response to the presence of a gaseous analyte, wherein the enclosure comprises a first aperture for permitting, in use, entry of ultra-violet radiation generated by a photoionisation detector lamp, and a second aperture for permitting, in use, ingress of a gaseous analyte, the gas cell further comprising an electrically isolated metal first filter for permitting, in use, diffusion controlled ingress of a gaseous analyte into the enclosure through the second aperture.
  • metal means pure metals and metal alloys, such as steel, which comprise trace amounts of non-metallic elements. A metal first filter has been found to be resistant to decomposition when exposed to ultra-violet radiation.
  • a photoionisation detector comprising a gas cell according to the first aspect of the invention and a photoionisation detector lamp.
  • Figure 1 which illustrates a gas cell in accordance with the first aspect of the invention comprising both a metal first filter and PTFE second filter;
  • FIG 2 which illustrates the gas cell of Figure 1 in exploded view but without the filters
  • FIG 3 which illustrates the results of tests of a photoionisation detector comprising the gas cell of Figure 2 with various combinations of metal first filter and PTFE second filter;
  • FIG. 4 which illustrates another photoionisation detector according to the second aspect of the invention without a PTFE second filter
  • FIG. 5 which illustrates a cross-section of part of the photoionisation detector of Figure 4 showing the location of the metal first filter.
  • a gas cell for a photon ionisation detector comprising an enclosure and at least one pair of cathode and anode electrodes at different electrical potentials for measuring a photoionisation current between the electrodes in response to the presence of a gaseous analyte, wherein the enclosure comprises a first aperture for permitting, in use, entry of ultra-violet radiation generated by a photoionisation detector lamp, and a second aperture for permitting, in use, ingress of a gaseous analyte, the gas cell further comprising an electrically isolated metal first filter for permitting, in use, diffusion controlled ingress of a gaseous analyte into the enclosure through the second aperture.
  • the metal first filter at least partially blocks egress of ultra-violet radiation from the gas cell through the second aperture.
  • the metal first filter is preferably in the form of a mesh, preferably that mesh is in the form of one of the group consisting of a Dutch weave, a twilled Dutch weave, and a reverse Dutch weave. It has been observed that a metal filter in the form of a fine woven mesh is particularly effective at providing diffusion controlled ingress of a gaseous analyte into the enclosure through the second aperture. Furthermore Dutch weave, twilled Dutch weave, or reverse Dutch weave provides the additional benefit of preventing egress of substantially all ultra-violet radiation from the gas cell. One advantage of this additional benefit is considerably extending the lifetime of any PTFE hydrophobic second filter placed over the top of the metal first filter.
  • the weave may be "light tight” blocking all direct ultra-violet radiation from passing through the weave, or “non-light tight” which will be partially effective at blocking direct ultra-violet radiation from passing through the weave and can be stacked in a manner so that gaps in the weave do not overlap to more effectively block direct ultra-violet radiation from passing through the metal first filter.
  • Ultra-violet radiation may also pass through the metal first filter by multiple internal reflections, but will emerge substantially attenuated.
  • a suitable metal first filter may be obtained from Locker Wire Weavers Limited of Warrington, Cheshire, UK.
  • the metal first filter has a ceramic coating facing towards the first aperture.
  • the ceramic coating is formed from alumina or silica, typically applied by vacuum deposition.
  • the metal first filter with a coating of ceramic facing towards the first aperture to suppress ejection of photoelectrons.
  • the coating thickness is in the range 1-6, preferably 2-6, most preferably 3-5 microns. It has been observed that above 6 microns in thickness, the ceramic coating is susceptible to breaking off the metal first filter, and below 1 micron in thickness, the ceramic coating is less effective at suppressing ejection of photoelectrons.
  • the ceramic coating coats all or only a portion of the metal first filter facing towards the first aperture.
  • the gas cell may further comprise a hydrophobic second filter which in use reduces or prevents ingress of water into the enclosure through the second aperture, wherein the metal first filter, in use, at least partially blocks ultra-violet radiation generated by a photon ionisation detector lamp from impinging upon the hydrophobic second filter.
  • the ingress of water into the enclosure is described in detail in previously mentioned US 7 046 012 B2 (Ion Science Limited).
  • condensation on the surrounds of the enclosure or electrode supports and extending between the electrodes provides an alternative route for electric current to flow between the electrodes producing a spurious signal which can obscure the small signal derived from photo-ions.
  • the hydrophobic second filter is formed of polytetrafluoroethylene.
  • a photoionisation detector comprising a gas cell according to the first aspect of the invention and a photoionisation detector lamp.
  • FIG. 1 illustrates a gas cell according to the first aspect of the invention comprising a metal first filter (101) in the form of a 0.06 mm thick 316 steel 400 x 2800 (wires per inch) Dutch weave mesh of 4.5 mm in diameter (available from Locker Wire Weavers Limited, Warrington, Cheshire, UK) and a 0.18 mm thick Porex PMV15 PTFE second filter (102) with a pore size of less than 0.4 microns (available from Porex Corporation, Fairburn, Georgia, US) which comprises an adhesive perimeter for securing both the metal first filter and PTFE second filter in place over the second aperture.
  • a metal first filter (101) in the form of a 0.06 mm thick 316 steel 400 x 2800 (wires per inch) Dutch weave mesh of 4.5 mm in diameter (available from Locker Wire Weavers Limited, Warrington, Cheshire, UK) and a 0.18 mm thick Porex PMV15 PTFE second filter (102) with a pore size of less than 0.4 microns
  • Figure 2 shows an exploded view of the gas cell without the first and second filters comprising a gas cell base (201), a photoionisation detector lamp seal (202), a anode electrode (203), a "Fence” electrode (204), an cathode electrode (205), a gas cell lid (206) and PTFE electrode spacers (207) and (208), and a sealing spacer (209).
  • the "Fence” electrode is set at a potential very close to the cathode electrode takes up almost all of the current due to condensation in the enclosure such that any remaining spurious signal due to condensation is small relative to the small signal derived from photo-ions.
  • the "Fence” electrode is described in detail in US 7 046 012 B2 (Ion Science Limited).
  • the photoionisation detector was placed in a gas switching cradle which enabled ultra-high purity air or 100 ppm isobutylene in ultra-high purity air to be presented to the second aperture at a flow rate of about 100 mL.bar/minute, and switched from one gas to the other at 60 s intervals.
  • the replacement of one gas with another was 99 % complete within 0.1 seconds.
  • the signal was measured with or without the metal first filter, with or without the PTFE second filter, and with a combination of both the metal first filter and PTFE second filter as shown in Figure 1.
  • Figure 4 and Figure 5 illustrate a second embodiment of the invention without a PTFE second filter.
  • Figure 4 illustrates an exploded view of a photoionisation detector comprising a printed circuit board stack assembly (401), a housing (402), a top cap (403), a photoionisation detector lamp (404) and a screening cap (405), the latter providing electrical contact with the housing which in turn is earthed to shield the photoionisation detector from high frequency electromagnetic radiation such as produced by mobile phones.
  • Figure 5 illustrates a cross section of the top cap of Figure 4 showing that the metal first filter (501) is recessed to avoid contact with the screening cap.

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Abstract

The invention relates to a gas cell for a photoionisation detector, in particular a gas cell for a photoionisation detector comprising an enclosure and an electrically isolated metal first filter for permitting, in use, diffusion controlled ingress of a gaseous analyte into the enclosure and a photoionisation detector comprising the said gas cell. In particular, a gas cell for a photoionisation detector is provided comprising an enclosure and at least one pair of cathode and anode electrodes at different electrical potentials for measuring a photoionisation current between the electrodes in response to the presence of a gaseous analyte, wherein the enclosure comprises a first aperture for permitting, in use, entry of ultra-violet radiation generated by a photoionisation detector lamp, and a second aperture for permitting, in use, ingress of a gaseous analyte, the gas cell further comprising an electrically isolated metal first filter for permitting, in use, diffusion controlled ingress of a gaseous analyte into the enclosure through the second aperture.

Description

A GAS CELL FOR A PHOTOIONISATION DETECTOR
The invention relates to a gas cell for a photoionisation detector, in particular a gas cell for a photoionisation detector comprising an enclosure and an electrically isolated metal first filter for permitting, in use, diffusion controlled ingress of a gaseous analyte into the enclosure and a photoionisation detector comprising the said gas cell.
Photoionisation detection engages ultra-violet radiation, of typical photon energies in the range 8 to 12 eV, to collide with a gaseous analyte, typically a volatile organic compound (VOC), causing its fragmentation into electrons and photo-ions, in a process known as photoionisation. In photoionisation detectors, photoionisation is usually confined by an enclosure which includes as one wall member one face of a crystal window through which the photoionising radiation is presented to the enclosure. A detector typical comprises at least two electrodes located within the enclosure connected by an electric circuit. In use, an electric field is generated between the electrodes causing the generated electrons and photo-ions to separate according to their electric charge and migrate to one of the two electrodes where their electric charge is neutralised by transfer of electrons to or from the electrodes. The resulting electric current which flows between the electrodes is amplified and output as a signal indicative of the concentration of photo-ions inside the enclosure.
If the enclosure is only partial and is substantially open to a gaseous environment, the signal due to a gaseous analyte is prone to instability. One reason for signal instability is that diffusion of the gaseous analyte near the open end of the enclosure is susceptible to natural air currents. It is therefore very typical for an enclosure to comprise a filter for permitting, in use, diffusion controlled ingress of the gaseous analyte into the enclosure.
The filter is typically formed from polytetrafluoroethylene (PTFE). PTFE is an appropriate material because it is readily available, not readily photo-ionised and does not significantly adsorb gaseous analytes such as VOCs which might otherwise cause a retarded response to both a positively and a negatively changing gaseous analyte concentration within the enclosure. Furthermore PTFE is resilient to the corrosive gases commonly encountered in environments where photoionisation detectors are often deployed, highly electrically resistive therefore not interacting with the electric field in the enclosure, and has a low dielectric constant and therefore highly repellent to water which may be presented to the detector in the form of condensation or smoke particles.
However it has been observed that over the course of a few months of illumination by the photoionisation detector lamp, the PTFE filter decomposes and vaporises. It is thought that the photo-ionising radiation itself is the agent for this destruction. Although filter life can be extended by deployment of a thicker filter, or by engaging 'sacrificial' materials together with the PTFE filter, such solutions add thickness to the filter thereby compromising the rate of response of the detector.
Various prior art arrangements of photoionisation detector are described in US 4 013 913 (HNU Systems Inc.), US 7 046 012 B2 (Ion Science Limited) and US 7 821 270 B2 (Ion Science Limited).
There is a desire to use photoionisation detectors in urban centres and municipal spaces to test air quality where such presents a risk to health and the environment. One requirement for such applications is that the detectors operate for a long time, maybe years, without human interference. Hence there is a need for detectors where the filter does not decompose.
Brief description of the invention
In a first aspect of the invention, a gas cell for a photon ionisation detector is provided, the gas cell comprising an enclosure and at least one pair of cathode and anode electrodes at different electrical potentials for measuring a photoionisation current between the electrodes in response to the presence of a gaseous analyte, wherein the enclosure comprises a first aperture for permitting, in use, entry of ultra-violet radiation generated by a photoionisation detector lamp, and a second aperture for permitting, in use, ingress of a gaseous analyte, the gas cell further comprising an electrically isolated metal first filter for permitting, in use, diffusion controlled ingress of a gaseous analyte into the enclosure through the second aperture. The term "metal" means pure metals and metal alloys, such as steel, which comprise trace amounts of non-metallic elements. A metal first filter has been found to be resistant to decomposition when exposed to ultra-violet radiation.
Surprisingly, it was observed, in use, that the ultra-violet radiation generated by photoionisation detector lamp impinging on the electrically isolated metal first filter did not cause ejection of photoelectrons at a level leading to a significant false photoionisation detector signal in air free of gaseous analyte such as photoionisable VOCs. Whilst not bound by theory, it is thought that this may be due to the build up of charge on the electrically isolated metal first filter inhibiting further ejection of photoelectrons.
In a second aspect of the invention, a photoionisation detector is provided, the photoionisation detector comprising a gas cell according to the first aspect of the invention and a photoionisation detector lamp.
Brief description of the figures
The invention is exemplified with reference to:
Figure 1 which illustrates a gas cell in accordance with the first aspect of the invention comprising both a metal first filter and PTFE second filter;
Figure 2 which illustrates the gas cell of Figure 1 in exploded view but without the filters;
Figure 3 which illustrates the results of tests of a photoionisation detector comprising the gas cell of Figure 2 with various combinations of metal first filter and PTFE second filter;
Figure 4 which illustrates another photoionisation detector according to the second aspect of the invention without a PTFE second filter; and
Figure 5 which illustrates a cross-section of part of the photoionisation detector of Figure 4 showing the location of the metal first filter. Detailed description of the invention
In a first aspect of the invention, a gas cell for a photon ionisation detector is provided, the gas cell comprising an enclosure and at least one pair of cathode and anode electrodes at different electrical potentials for measuring a photoionisation current between the electrodes in response to the presence of a gaseous analyte, wherein the enclosure comprises a first aperture for permitting, in use, entry of ultra-violet radiation generated by a photoionisation detector lamp, and a second aperture for permitting, in use, ingress of a gaseous analyte, the gas cell further comprising an electrically isolated metal first filter for permitting, in use, diffusion controlled ingress of a gaseous analyte into the enclosure through the second aperture.
Preferably, in use, the metal first filter at least partially blocks egress of ultra-violet radiation from the gas cell through the second aperture.
The metal first filter is preferably in the form of a mesh, preferably that mesh is in the form of one of the group consisting of a Dutch weave, a twilled Dutch weave, and a reverse Dutch weave. It has been observed that a metal filter in the form of a fine woven mesh is particularly effective at providing diffusion controlled ingress of a gaseous analyte into the enclosure through the second aperture. Furthermore Dutch weave, twilled Dutch weave, or reverse Dutch weave provides the additional benefit of preventing egress of substantially all ultra-violet radiation from the gas cell. One advantage of this additional benefit is considerably extending the lifetime of any PTFE hydrophobic second filter placed over the top of the metal first filter. The weave may be "light tight" blocking all direct ultra-violet radiation from passing through the weave, or "non-light tight" which will be partially effective at blocking direct ultra-violet radiation from passing through the weave and can be stacked in a manner so that gaps in the weave do not overlap to more effectively block direct ultra-violet radiation from passing through the metal first filter. Ultra-violet radiation may also pass through the metal first filter by multiple internal reflections, but will emerge substantially attenuated. A suitable metal first filter may be obtained from Locker Wire Weavers Limited of Warrington, Cheshire, UK. Preferably the metal first filter has a ceramic coating facing towards the first aperture. Preferably the ceramic coating is formed from alumina or silica, typically applied by vacuum deposition. Although it was observed, in use, that the ultra-violet radiation generated by photoionisation detector lamp impinging on the electrically isolated metal first filter did not cause ejection of photoelectrons at a level leading to a significant false photoionisation detector signal in air free of gaseous analyte, it is considered advantageous to provide the metal first filter with a coating of ceramic facing towards the first aperture to suppress ejection of photoelectrons. Typically the coating thickness is in the range 1-6, preferably 2-6, most preferably 3-5 microns. It has been observed that above 6 microns in thickness, the ceramic coating is susceptible to breaking off the metal first filter, and below 1 micron in thickness, the ceramic coating is less effective at suppressing ejection of photoelectrons. The ceramic coating coats all or only a portion of the metal first filter facing towards the first aperture.
The gas cell may further comprise a hydrophobic second filter which in use reduces or prevents ingress of water into the enclosure through the second aperture, wherein the metal first filter, in use, at least partially blocks ultra-violet radiation generated by a photon ionisation detector lamp from impinging upon the hydrophobic second filter.
The ingress of water into the enclosure is described in detail in previously mentioned US 7 046 012 B2 (Ion Science Limited). In summary condensation on the surrounds of the enclosure or electrode supports and extending between the electrodes provides an alternative route for electric current to flow between the electrodes producing a spurious signal which can obscure the small signal derived from photo-ions. Preferably the hydrophobic second filter is formed of polytetrafluoroethylene.
By at least partially blocks ultra-violet radiation generated by a photon ionisation detector lamp from impinging upon the hydrophobic second filter, the life of the hydrophobic second filter is extended. In a second aspect of the invention, a photoionisation detector is provided, the photoionisation detector comprising a gas cell according to the first aspect of the invention and a photoionisation detector lamp.
Example 1
A gas cell, as shown in Figure 1 and Figure 2 was fitted with a 10.6 eV photoionisation detector lamp. Figure 1 illustrates a gas cell according to the first aspect of the invention comprising a metal first filter (101) in the form of a 0.06 mm thick 316 steel 400 x 2800 (wires per inch) Dutch weave mesh of 4.5 mm in diameter (available from Locker Wire Weavers Limited, Warrington, Cheshire, UK) and a 0.18 mm thick Porex PMV15 PTFE second filter (102) with a pore size of less than 0.4 microns (available from Porex Corporation, Fairburn, Georgia, US) which comprises an adhesive perimeter for securing both the metal first filter and PTFE second filter in place over the second aperture. Figure 2 shows an exploded view of the gas cell without the first and second filters comprising a gas cell base (201), a photoionisation detector lamp seal (202), a anode electrode (203), a "Fence" electrode (204), an cathode electrode (205), a gas cell lid (206) and PTFE electrode spacers (207) and (208), and a sealing spacer (209). The "Fence" electrode is set at a potential very close to the cathode electrode takes up almost all of the current due to condensation in the enclosure such that any remaining spurious signal due to condensation is small relative to the small signal derived from photo-ions. The "Fence" electrode is described in detail in US 7 046 012 B2 (Ion Science Limited).
The photoionisation detector was placed in a gas switching cradle which enabled ultra-high purity air or 100 ppm isobutylene in ultra-high purity air to be presented to the second aperture at a flow rate of about 100 mL.bar/minute, and switched from one gas to the other at 60 s intervals. The replacement of one gas with another was 99 % complete within 0.1 seconds. The signal was measured with or without the metal first filter, with or without the PTFE second filter, and with a combination of both the metal first filter and PTFE second filter as shown in Figure 1.
The results are illustrated in Figure 3 and summarised in Table 1. It was observed that the metal first filter delivered approximately the same response to the test gas (100 ppm isobutylene) compared to ultra-high purity air as the PTFE second filter, both adding about 10 seconds to the T99 fall (i.e., to reach within 1 % of the signal baseline from the peak response considered 100 % rise), and that the effect on absolute gas responsivity (at 100 ppm) of the metal first filter (-5.5 %) decreased by more than the PTFE second filter (-3%), but not unacceptably so. Noise levels were similar in all cases at around 7-10 ppb for 1 sigma, so an expected peak to peak noise level of around +/- 30 ppb (about 3 sigma).
Table 1: Summary data from Figure 3.
Figure imgf000008_0001
Example 2
Figure 4 and Figure 5 illustrate a second embodiment of the invention without a PTFE second filter. Figure 4 illustrates an exploded view of a photoionisation detector comprising a printed circuit board stack assembly (401), a housing (402), a top cap (403), a photoionisation detector lamp (404) and a screening cap (405), the latter providing electrical contact with the housing which in turn is earthed to shield the photoionisation detector from high frequency electromagnetic radiation such as produced by mobile phones. Figure 5 illustrates a cross section of the top cap of Figure 4 showing that the metal first filter (501) is recessed to avoid contact with the screening cap.

Claims

Claims
1. A gas cell for a photoionisation detector comprising an enclosure and at least one pair of cathode and anode electrodes at different electrical potentials for measuring a photoionisation current between the electrodes in response to the presence of a gaseous analyte, wherein the enclosure comprises a first aperture for permitting, in use, entry of ultra-violet radiation generated by a photoionisation detector lamp, and a second aperture for permitting, in use, ingress of a gaseous analyte, the gas cell further comprising an electrically isolated metal first filter for permitting, in use, diffusion controlled ingress of a gaseous analyte into the enclosure through the second aperture.
2. A gas cell according to claim 1 wherein in use the metal first filter at least partially blocks egress of ultra-violet radiation from the gas cell through the second aperture.
3. A gas cell according to claim 2 wherein the metal first filter is in the form of a mesh.
4. A gas cell according to claim 3 wherein the mesh is in the form of one of the group consisting of a Dutch weave, a twilled Dutch weave, and a reverse Dutch weave.
5. A gas cell according to any one of the preceding claims, wherein the metal first filter comprises a ceramic coating facing towards the first aperture.
6. A gas cell according to claim 5, wherein the ceramic coating is formed of alumina or silica.
7. A gas cell according to any one of claims 2 to 6 further comprising a hydrophobic second filter for in use reducing or preventing ingress of water into the enclosure through the second aperture, wherein the metal first filter, in use, at least partially blocks ultra-violet radiation generated by a photon ionisation detector lamp from impinging upon the hydrophobic second filter.
8. A gas cell according to claim 7 wherein the hydrophobic second filter is formed of polytetrafluoroethylene.
9. A photoionisation detector comprising a gas cell according to any one of the preceding claims and a photoionisation detector lamp.
PCT/GB2020/050393 2019-02-20 2020-02-19 A gas cell for a photoionisation detector WO2020169967A1 (en)

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4013913A (en) 1976-01-19 1977-03-22 Hnu Systems Inc. Ion detection electrode arrangement
US7046012B2 (en) 2001-11-20 2006-05-16 Ion Science Limited Ionization devices
CN1818633A (en) * 2006-03-17 2006-08-16 中国科学院安徽光学精密机械研究所 Portable ionization chamber of photoionization detector
CN101603945A (en) * 2009-07-13 2009-12-16 中北大学 Portable photo-ionization gas detector
US7821270B2 (en) 2007-05-30 2010-10-26 Ion Science Limited Electrode contact pellet and associated photoionisation detector assembly
US20160362787A1 (en) * 2015-06-15 2016-12-15 Inficon, Inc. Process gas management system and photoionization detector

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4013913A (en) 1976-01-19 1977-03-22 Hnu Systems Inc. Ion detection electrode arrangement
US7046012B2 (en) 2001-11-20 2006-05-16 Ion Science Limited Ionization devices
CN1818633A (en) * 2006-03-17 2006-08-16 中国科学院安徽光学精密机械研究所 Portable ionization chamber of photoionization detector
US7821270B2 (en) 2007-05-30 2010-10-26 Ion Science Limited Electrode contact pellet and associated photoionisation detector assembly
CN101603945A (en) * 2009-07-13 2009-12-16 中北大学 Portable photo-ionization gas detector
US20160362787A1 (en) * 2015-06-15 2016-12-15 Inficon, Inc. Process gas management system and photoionization detector

Non-Patent Citations (1)

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Title
MILLIPORE CORPORATION: "Filter Integrity Test Methods Introduction", 21 April 2020 (2020-04-21), pages 1 - 12, XP055688575, Retrieved from the Internet <URL:https://elsmar.com/elsmarqualityforum/attachments/tb039-pdf.15664/> [retrieved on 20200423] *

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