Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
  • G01N30/02—Column chromatography
  • G01N30/62—Detectors specially adapted therefor
  • G01N30/64—Electrical detectors
  • G01N30/68—Flame ionisation detectors
• • 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
  • G01N27/626—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 heat to ionise a gas
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
  • G01N30/02—Column chromatography
  • G01N30/60—Construction of the column
  • G01N30/6095—Micromachined or nanomachined, e.g. micro- or nanosize

Definitions

• the invention relates to a flame ionization detector (FID) comprising a fuel gas supply and igniter, a sample gas supply, a combustion chamber in which the sample gas is ionized by the flame, and electrodes to generate and measure the ionic current a voltage is applied.
• FID flame ionization detector
• Flame ionization detectors serve to detect and measure volatile organic compounds in gaseous samples. The measurement is based on the chemical ionization of organic substances which are pyrolyzed in a oxyhydrogen flame. An ionization reaction of the carbon atoms contained in the substance takes place:
• a voltage is applied to an electrode pair arranged at the edge of the flame, an ion current flows which can be measured and used to detect the organic compounds. If the gas first passes through a gas chromatograph, for example a capillary gas chromatograph, then the various chemical compounds of the sample gas, sorted by molecular weight, enter the flame ionization detector one after the other, so that the concentration tion of the various components can be determined.
• a gas chromatograph for example a capillary gas chromatograph
• a problem with flat ionization detectors is that oxyhydrogen gas must be supplied to a high explosive mixture of oxygen and hydrogen. It is therefore desirable to make the flame ionization detectors as small as possible so that only small amounts of oxyhydrogen are needed and the risk of explosion is thereby reduced. In addition, such small flame ionization detectors are of course beneficial because they are easier to transport and require less space. Further, because of the lower consumption of oxyhydrogen gas, it is not possible to use it in stored form but to produce it locally by electrolysis, further reducing the risk of explosion.
• Such a flame ionization detector making use of this advantage consists of components which are manufactured according to the methods of microsystem technology (Zimmermann, S. et al., "Micro flame ionization detector and microflame spectrometer", Sensors and Actuators B63 (2000). Zimmermann et al., Miniaturized Flame Ionization Detector for Gas Chromatography, Sensors and Actuators B83 (2002), pp. 285-289).
• the oxyhydrogen flame burns in the open space and is surrounded only by a metallized glass tube, which forms an electrode pair together with the silicon substrate. As the flame burns in open space, the result can be affected by turbulence and impurities.
• the object of the invention is to provide a flat ionization detector which has a small size and can be manufactured completely by the methods of microsystem technology.
• the flame ionization detector is characterized in that it is constructed as an integrated planar system of at least three parallel interconnected platelet-shaped substrates, which are processed by microsystem technology, a middle substrate having nozzles for the gases and the ignition device and a recess, which forms a part of the combustion chamber, which is completed by recesses in the adjacent substrates and is closed by these substrates substantially together with the nozzle region, and the adjacent substrates have feed channels for the gases.
• the flame ionization detector according to the invention thus essentially consists of three platelet-shaped substrates, although further substrates could be provided. These substrates are produced exclusively by the means of microsystem technology by photoetching and the like.
• the middle substrate has nozzles for the gas se and the ignition device and a recess which forms a part of the combustion chamber.
• the combustion chamber is completed by recesses in the adjacent substrates. While the central substrate may be completely broken in the region of the combustion chamber, the adjacent substrates have depressions which close the combustion chamber after assembly, so that the combustion chamber is substantially closed.
• Essentially closed means that the combustion chamber must have only a small opening through which the gases can escape to the outside, and one could even consider completely closing the combustion chamber if a cooling device is provided on which the combustion chamber condensate, which would then only have to be taken to ensure that the water is removed.
• the two adjacent or outer substrates not only surround the combustion chamber, but also the nozzle area. While the nozzles for the fuel gas and the sample gas are provided in the middle substrate, the supply of these gases is effected by feed channels in the adjacent o- and outer substrates.
• the middle substrate is conductive and the adjacent substrates are substantially non-conductive.
• Essentially non-conductive means that the conductivity is low, even at elevated temperatures, but so high that anodic bonding of the substrates is possible, which presupposes a certain conductivity of the components, but this conductivity should not be too high be, because not only ionic currents that are to be measured, but also leakage currents take place through the substrate, which can falsify the measurement result.
• one ⁇ -reflector is arranged in each case in the region of the combustion chamber in the adjacent substrates. So there are electrodes on both sides of the combustion chamber.
• the disadvantage is that when a voltage is applied to the two electrodes, not only the ion current is measured, but also the current flowing from one electrode to another due to the non-zero conductivity of the outer substrates and water flows, which has settled.
• a protective electrode according to the invention through which these currents are absorbed.
• an electrode is formed by the middle substrate and, on the other hand, the protective electrode is located next to the second electrode on one of the two adjacent substrates, between the two electrodes. Currents flowing from one adjacent substrate to the other adjacent substrate are in this case picked up by the guard electrode and not measured.
• the flame ionization detector Due to the high temperature of the flame (up to 2700 0 C), the flame ionization detector is strongly heated. To voltage To avoid cracks, expediently all parts have rounded contours.
• the nozzles for the gases are formed as a buried structure and covered by at least one further substrate. In this way one can achieve symmetrical arrangement of the nozzles.
• the middle substrate has an electrode tip immediately behind the nozzles. About this electrode tip and an electrode on one of the two adjacent substrates, a high voltage pulse for igniting the flame can be applied. Such a high voltage pulse could be generated for example by a piezo crystal.
• the flame ionization detector can also be used to generate electrical energy by providing it with two high induction magnets, thereby forming a magnetohydrodynamic generator.
• Fig. 1 shows an exploded view of an embodiment of the flame ionization detector according to the invention
• Fig. 2 is a sectional view taken along the angled line A-A'-A '' of Fig. 1;
• FIG. 3 is a sectional view corresponding to FIG. 2 of a measuring arrangement
• FIG. 4 shows a section, in a corresponding representation as in FIG. 2, of a second particularly advantageous embodiment of the measuring arrangement
• Fig. 5 shows the dependence of the ion current on the applied voltage in an advantageous embodiment
• Fig. 6 shows the dependence of the ion current of the
• FIG. 1 shows an exploded view of an embodiment of the flame ionization detector according to the invention. It comprises three substrates, a middle substrate 1 made of silicon and a lower substrate 2 and an upper substrate 3 made of pyrex glass. A part of the combustion chamber 4, the sample gas nozzle 5 and the fuel gas nozzle 6 are worked out into the middle silicon substrate 1 by known methods of microsystem technology. Tip-shaped projections 7, which protrude into the combustion chamber 4 in the vicinity of the nozzles 5, 6, can be acted upon by a high-voltage pulse for ignition.
• the lower substrate 2 and the upper substrate 3 are provided in the region of the combustion chamber 4 with trough-shaped recesses, which are provided with a reflective metallization 8.
• the metallization 8 is in this case with bonding islands 9 connected, can take place via the electrical connection.
• the lower substrate 2 in the figures also has a fuel gas inlet 10, while the upper substrate 3 has a sample gas inlet 11. These inlets, after the three substrates are connected by anodic bonding, are in communication with the nozzles 5, 6.
• Fig. 2 is a sectional view taken along the angled line A-A '-A' 'of Fig. 1 is shown.
• the fuel gas and the sample gas enter through suitable channels in the combustion chamber 4, which is provided with the metallizations 8.
• These metallizations can be used as the electrodes to which a voltage is applied and the current is measured, as shown schematically in FIG.
• a disadvantage is that not only an ion current between the two electrodes 8 is generated by the voltage source U, which is measured at I, but on the one hand, a current due to the limited conductivity of the substrates 1, 2 and 3 and a current passing through low moisture is effected.
• a protective electrode 12 Only one of the metallizations 8, namely the lower one in FIG. 12, is electrically connected. The other metallization has the sole purpose of reflecting heat back into the combustion chamber 4, so that less fuel gas is needed.
• the substrate 1 serves as a second electrode for the measurement.
• the protective electrode 12 is connected to the substrate 1 via the voltage source U. Currents that flow outside the combustion chamber (before the gases reach the combustion chamber), namely because of the conductivity of the substrates and deposited water, although due to the voltage source U, but by the Ammeter I not measured. Rather, only the currents between substrate 1 and lower electrode 8 are measured, that is to say only the currents which actually result from the flame ionization.
• the flame ionization detector according to the invention can be made very small. Typically, it occupies a footprint of 10 x 10 mm.
• the substrates need only have a thickness of a few 100 microns.
• the nozzle openings for the fuel gas and the measurement gas can be reduced to a few 10 to 100 microns 2 , so as to minimize the fuel gas consumption or to optimize the gas mixture.
• the combustion chamber 4 is shown open to the right in the figures, it is normally closed except for a small opening to avoid turbulence due to external air currents and contaminants.
• the back diffusion from the environment can be prevented, for example, by the combustion chamber 4 communicating with the environment only through a narrow gap, for instance between the middle and one or both adjacent cover substrates or through a small gap in the middle substrate.
• the combustion chamber could be completely closed with water in which the combustion product, namely water, condenses on an additional cooling device.
• the production of the flame ionization detector can, as mentioned, be carried out with the customary techniques of microsystem technology and photolithography.
• a typical flame ionization detector according to the invention operates at relatively low voltages, as shown in FIG. Already at a voltage of plus or minus 50 V, saturation occurs. The measurement result is then constant at higher voltage levels. The corresponding curve was recorded with a sample gas flow of 7 ml / min. The dependence of the ion current on the flow rate of the sample gas at a voltage of 100 V is shown in FIG.

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• Chemical & Material Sciences (AREA)
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• Health & Medical Sciences (AREA)
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• Other Investigation Or Analysis Of Materials By Electrical Means (AREA)

Priority Applications (5)

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• 2007
  • 2007-09-13 EP EP07018014A patent/EP2037264A1/de not_active Withdrawn
• 2008
  • 2008-08-18 WO PCT/EP2008/006781 patent/WO2009036854A1/de not_active Ceased
  • 2008-08-18 CA CA2699230A patent/CA2699230C/en not_active Expired - Fee Related
  • 2008-08-18 EP EP08785606A patent/EP2191263B1/de not_active Not-in-force
  • 2008-08-18 JP JP2010524370A patent/JP5427178B2/ja not_active Expired - Fee Related
  • 2008-08-18 US US12/675,470 patent/US8305086B2/en not_active Expired - Fee Related
  • 2008-08-18 CN CN200880108178.0A patent/CN101836111B/zh not_active Expired - Fee Related

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