JP2018021767A - Device and method for detecting volatile organic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and method for detecting a volatile organic, capable of improving the determination accuracy of gas including the volatile organic by determining the concentration and diffusion constant of the volatile organic and controlling the amounts of travel of charged particles in the inner wall of a volatile organic detection chamber.SOLUTION: A device for detecting a volatile organic comprises: ionization energy supply means 14; a pair of ion detection electrodes 16; a detection chamber 12 including the ion detection electrodes; voltage applying means 18 capable of reversing the polarity of a voltage applied to the ion detection electrodes; current measuring means 20 for measuring the value of a current flowing through the ion detection electrodes; diffusion constant calculation means 22 for calculating the diffusion constant of the volatile organic from a current ratio on the basis of current values before and after the reverse of voltage polarity; and inner wall voltage applying means capable of applying a voltage lower than the voltage applied to the ion detection electrodes to a detection chamber inner wall 24 constituted of a conductor and of reversing the voltage polarity. The ionization energy supply means is placed at a position generating a range having no supply of ionization energy, between the ion detection electrodes.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a volatile organic substance detector and a volatile organic substance detection method for detecting a volatile organic substance contained in an object to be measured, in particular, by ionizing the volatile organic substance and determining the size of the diffusion constant. The present invention relates to a volatile organic substance detector and a volatile organic substance detection method for stabilizing an ion detection technique for specifying the type of volatile organic substance contained in a target.

  Conventionally, in order to measure the concentration of a volatile organic substance or the like contained in a measurement object, a volatile organic substance detector such as a Photo Ionization Detector (hereinafter referred to as PID) has been used. The measurement principle of this PID is to induce a volatile organic substance to be measured in an apparatus in which a pair of application electrodes are arranged, and to irradiate a short wavelength ultraviolet ray (UV) to ionize the volatile organic substance, By capturing the ions with an applied electrode, a detection current having a correlation with the concentration is measured, and by converting the current value into a concentration, the concentration of a volatile organic substance or the like is measured.

  As shown in FIG. 8 as an example, the PID 50 applies a voltage to the detection chamber 52 into which volatile organic substances and the like are introduced and discharged, a pair of electrodes 54 provided in the detection chamber 52, and the electrode 54. Applying circuit 56, UV lamp unit 58 for irradiating the measurement fluid (FL) in detection chamber 54 with UV, measurement circuit 60 for measuring the current flowing through electrode 54, and further, from the current value, volatile organic substances, etc. The computer 62 includes a calculation device 62 that performs a calculation for conversion into a concentration.

  In this conventional PID, a single-component volatile organic substance or the like is introduced into the detection chamber 52 and discharged from the detection chamber 52 after UV irradiation by the UV lamp unit 58. The introduced volatile organic matter or the like is ionized by UV irradiated from the UV lamp unit 58 provided on the side wall portion of the detection chamber 52, and a voltage provided in the detection chamber 52 is applied to the ions or electrons. By being attracted to and captured by the electrode 54, a current is generated in the circuit.

  Then, this current is measured by the measurement circuit 60, and further, the calculation device 62 multiplies the current value by a coefficient for each substance (a substance such as a volatile organic substance to be measured), thereby obtaining a volatile organic substance or the like. Is output. Since such PID is sensitive to many volatile organic substances as in the other detectors and detection methods described above, it is an effective means for measuring volatile organic substances, and the apparatus itself is also large. Therefore, it is possible to easily measure volatile organic substances and the like, which is very useful.

  Subsequently, as a conventional PID, for example, Patent Document 1 discloses a substrate including a gas ionization chamber, at least one ion detection electrode pair, and at least one amplifier circuit, and an ultraviolet (UV) light beam. At least one UV ionization source for delivery into the gas ionization chamber within the at least one amplification circuit and the at least one ion sensing electrode pair having an electrical guard ring for reducing leakage current signals. A built-in photoionization detector (PID) is disclosed.

  Furthermore, Patent Document 2 discloses a structure that prevents leakage current due to ions by providing a barrier electrode between ion detection electrodes in an ion detection device. And in patent document 3, the filament which ionizes the trace amount sodium etc. in gas by thermal dissociation through the insulation bushing in the housing | casing which distribute | circulates analyte gas, and the collector electrode which collects the produced | generated ions are provided. In this configuration, there is disclosed a trace ion detector characterized by providing an annular guard electrode that is bent around the collector electrode and held at the same potential as the collector electrode. The leakage current that flows constantly can be removed.

  Furthermore, as a conventional PID, Patent Document 4 discloses at least ionization energy supply means for supplying ionization energy to the volatile organic substance and detecting the ionized ions in order to ionize the volatile organic substance. A pair of ion detection electrodes; voltage application means for applying a predetermined voltage to the ion detection electrodes; voltage measurement means capable of reversing voltage polarity; current measurement means for measuring a current value flowing through the ion detection electrodes; A diffusion constant calculating means for calculating a diffusion constant of the volatile organic substance from a current ratio based on a current value before and after the voltage polarity reversal measured by the current measuring means when the voltage polarity is reversed by the applying means. The ionization energy supply means is arranged between the ion detection electrodes and within a range biased to one of the ion detection electrodes. A volatile organic substance detector is disclosed in which a range in which the ionization energy is not supplied is generated between the ion detection electrodes by being provided to supply energy. By providing the UV region, the ion species can be discriminated.

JP 2012-118063 A International Publication No. 2003/046535 JP-A-57-91449 Japanese Patent No. 5779038

  However, in the configuration of the technique disclosed in Patent Documents 1 to 3, the inner wall of the ion detection chamber is made of an insulating material, and the surface of the insulator due to the adhesion of ions to the insulator, the application of voltage to the ion detection electrode, or the like. Although it is possible to stabilize the current flowing to the ion detection electrode by providing a guard electrode that removes leakage current generated in the case, when the detection chamber is large and the inner wall surface area is large, electrons with high mobility, Since the oxygen molecular ions reach the positive electrode quickly and disappear, the detection chamber contains a large number of volatile organic cation ions.

  Then, a large number of positive ions accumulate (charge) locally or in an island shape on the inner wall, and the number and location change with time, so the flight speed of ions depends on the charge on the inner wall surface. In addition, the amount of ions fluctuates and the concentration detection current becomes unstable. Note that the techniques disclosed in Patent Documents 1 to 3 do not have a structure for determining a substance. In addition, the technique disclosed in Patent Document 4 is provided with an ion flight channel (non-UV region) that is not irradiated with UV between electrodes, so that the detection chamber is large, and the concentration detection current is not stable as described above. There is.

  The problem to be solved by the present invention is to cope with the above-mentioned problem, and the size of the diffusion constant, which is an important property of the volatile organic substance, together with the concentration of the volatile organic substance with a simple configuration and a small apparatus. Volatile organic matter detector and volatile organic substance detector capable of improving the discrimination accuracy of gas containing volatile organic matter by controlling the amount of movement of charged particles on the inner wall of the volatile organic matter detection chamber It is to provide a method for detecting an organic substance.

In order to solve the above-described problems, the present invention takes the following technical means.
That is, the invention according to claim 1 is an ionization energy supply means for supplying ionization energy to the volatile organic matter in order to ionize the volatile organic matter, and at least one pair of ions for detecting the ionized ions. A detection electrode; a detection chamber containing the ion detection electrode; a voltage applying means capable of reversing a voltage polarity for applying a predetermined voltage to the ion detection electrode; and a value of a current flowing through the ion detection electrode. A diffusion for calculating a diffusion constant of the volatile organic substance from a current ratio based on a current value before and after the voltage polarity reversal measured by the current measuring unit when the voltage polarity is reversed by the current measuring unit and the voltage applying unit. Constant ion calculation means, and the ionization energy supply means is biased to one ion detection electrode between the ion detection electrodes In the volatile organic matter detector in which the ionization energy is not supplied between the ion detection electrodes by supplying the ionization energy to the enclosure, the inner wall of the detection chamber is made of a conductor. The inner wall of the detection chamber is made of a conductor, and an inner wall voltage applying unit capable of reversing the voltage polarity for applying a voltage lower than the voltage applied to the ion detection electrode to the inner wall is provided. This is a volatile organic substance detector.

  The invention described in claim 2 is the volatile organic substance detector according to claim 1, wherein the ionization energy supply means is a UV irradiation means for irradiating the volatile organic substance with UV, and the volatile organic substance. One of an ionizing radiation emitting unit that emits ionizing radiation and a corona discharge unit that causes corona discharge to the volatile organic substance is provided.

  The invention according to claim 3 is an ionization process for supplying ionization energy to a volatile organic substance flowing into a detection chamber having an inner wall made of a conductor to ionize the volatile organic substance, and the ionization process. An ion detection step of detecting ions ionized by at least one pair of ion detection electrodes to which a predetermined voltage is applied, and lower than a predetermined voltage applied to the ion detection electrode with respect to the inner wall Before and after the inversion, the polarity of the voltage applied to the electrode for ion detection is reversed, and the current value measurement step for measuring the current value flowing through the electrode for ion detection is reversed. Diffusion constant calculation for obtaining a current ratio from a current value flowing through the ion detection electrode and calculating a diffusion constant of the volatile organic substance from the current ratio When the polarity of the voltage applied to the ion detection electrode is reversed in the diffusion constant calculating step, the inner wall for determining the polarity of the voltage applied to the inner wall in the inner wall voltage applying step. A voltage application reversal step, wherein the ionization step is performed between the ion detection electrodes and supplies the ionization energy to a range biased to one of the ion detection electrodes. It is a volatile organic matter detection method characterized by generating a range in which the ionization energy is not supplied between electrodes and supplying ionization energy to the volatile organic matter.

  According to the volatile organic matter detector and the volatile organic matter detection method according to the present invention, the inner wall of the detection chamber is a conductor, and further, a predetermined voltage can be applied to the detection chamber wall. Charged particles do not accumulate on the detection chamber wall, and stable ion current measurement can be performed.

  Further, according to the volatile organic substance detector and the volatile organic substance detection method according to the present invention, the size of the diffusion constant effective for specifying the type of the volatile organic substance is determined based on the current value flowing through the detection electrode that detects ions. Can be obtained. It is also possible to estimate volatile organic substances from the diffusion constant. Furthermore, since it is possible to obtain not only the concentration of volatile organic substances but also the diffusion constant, for example, it is easy to obtain information on ventilation guidelines for factories and the like. Furthermore, since the volatile organic substance detector itself does not require a complicated configuration, it can be used as a simple and small-sized one.

It is the schematic diagram which showed an example of the structure of the detector in embodiment of the volatile organic substance detector which concerns on this invention. It is an example figure which showed the detection process in embodiment of the volatile organic substance detection method which concerns on this invention. It is a schematic diagram which shows the arrangement | positioning of an electrode, the UV irradiation position, and the application condition of a voltage for demonstrating the theory of the diffusion constant calculation of the volatile organic substance in embodiment of the volatile organic substance detector and volatile organic substance detection method which concern on this invention. , (A) represents a state in which + volt is applied to the electrode, and (b) represents a state in which −volt is applied to the electrode. The schematic diagram which showed an example of the structure at the time of experimenting using the detector in embodiment of the volatile organic substance detector and volatile organic substance detection method concerning this invention, (a) is a non-UV cation. A state where the region is flying, (b) shows a state where the anion is flying in the non-UV region. In the embodiment of the volatile organic substance detector and the volatile organic substance detection method according to the present invention, the inner wall applied voltage when o-xylene (40 ppm on a dry air basis, flow rate 400 mL / min) is detected as the volatile organic substance. It is the graph which showed the experimental result of the relationship of positive ion current. In the embodiments of the volatile organic substance detector and the volatile organic substance detection method according to the present invention, ions when benzene and p-xylene (40 ppm on a dry air basis, flow rate 400 mL / min) are detected as volatile organic substances. It is the graph which showed the time change of electric current ratio, (a) represents what is based on the conventional detector, (b) represents what is based on this embodiment. In the embodiments of the volatile organic substance detector and the volatile organic substance detection method according to the present invention, benzene, o-xylene, and p-xylene (40 ppm on a dry air basis, flow rate 400 mL / min) are detected as volatile organic substances. 6 is a graph showing the relationship between the inner wall applied voltage (guard voltage) and the ionic current ratio. It is the schematic diagram which showed an example of the structure of the conventional PID. It is the graph which showed the result of the comparison experiment of embodiment of the volatile organic substance detector which concerns on this invention, and the electric current value between the ion detection electrodes in the conventional PID.

Subsequently, embodiments of the volatile organic substance detector and the volatile organic substance detection method according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing an example of the configuration of a detector in an embodiment of a volatile organic substance detector according to the present invention, and FIG. 2 shows a detection process in an embodiment of a volatile organic substance detection method according to the present invention. FIG. Further, 10 is a volatile organic substance detector, 12 is an ion detection chamber, 14 is a UV lamp, 16 is an ion detection electrode, 18 is a voltage application means, 20 is a current measurement means, 22 is a diffusion constant calculation means, and 24 is a detection chamber. A wall 26 indicates an inner wall voltage applying means.

  First, as shown in FIG. 1, the volatile organic substance detector 10 has an ion detection chamber 12 into which a volatile organic substance to be measured flows, and the ion detection chamber 12 has a volatile organic substance on its inner wall. A UV lamp 14 (ionization energy supply means) for supplying ionization energy is connected.

  The ion detection chamber 12 is provided with at least one pair of ion detection electrodes 16 for capturing ions of a volatile organic material ionized by ionization energy. In addition, as the ion detection electrode 16, a stainless electrode, a gold electrode, a platinum electrode, a copper electrode, or the like can be used.

  In the present embodiment, as shown in FIG. 1, the UV lamp 14 is provided between the electrodes of the ion detection electrodes 16 and at a position for supplying ionization energy to a range biased to one of the ion detection electrodes 16. Thus, a range in which ionization energy is not supplied between the electrodes of the ion detection electrode 16 is formed.

  Subsequently, to the ion detection electrode 16, a voltage application unit 22 that can apply a predetermined voltage to the ion detection electrode 16 is connected. Similarly, a current measurement unit 20 is also connected, A voltage is applied by the voltage application means 18 so that the value of the current flowing through the ion detection electrode 16 can be measured.

  The voltage application means 18 is configured to be able to reverse the voltage polarity. From the current ratio of the current value flowing through the ion detection electrode 16 measured by the current measurement means 20 before and after the voltage polarity inversion, A diffusion constant calculating means 22 capable of calculating the diffusion constant of the volatile organic substance to be measured is connected to the current measuring means 20. Then, the type of the volatile organic substance specified by the calculated diffusion constant is displayed by display means (not shown) connected to the diffusion constant calculation means 22.

  In addition, the concentration of the volatile organic substance to be measured can also be calculated based on the value of the current flowing through the ion detection electrode 16 measured by the current measuring means 20. As the calculation method, for example, in the case of toluene, data obtained by an experiment is accumulated in a storage device (not shown) in advance, and calculation is performed using the data.

  Furthermore, for example, when a gas to be measured contains a plurality of types of volatile organic substances, the calculated diffusion constant is calculated as an average value of the plurality of types of volatile organic substances. If an average value is displayed, it will be useful as a guideline for ventilation. Moreover, you may display with the density | concentration of the calculated volatile organic substance.

  In this embodiment, the ionization energy is supplied to the volatile organic substance by a UV lamp. However, this may be configured to irradiate the volatile organic substance with ionizing radiation, or corona is applied to the volatile organic substance. It is good also as a structure which causes discharge.

  Subsequently, in the volatile organic substance detector 10 according to the present embodiment, the detection chamber wall 24 of the ion detection chamber 12 is made of a conductor, and further, ions are detected with respect to the inner wall (detection chamber wall 24) of the ion detection chamber 12. Inner wall voltage application means 26 for applying a voltage lower than the voltage applied to the detection electrode 16 is provided. By adopting such a configuration, accumulation of charged particles does not occur on the inner wall, so that most of ions move to the inner wall of the ion detection chamber 12 (detection chamber wall 24) rather than the ion detection electrode 16. It is possible to keep the ion detection sensitivity and to measure the ion current more stably. Note that the voltage polarity of the inner wall voltage application means 26 can be reversed. When the voltage polarity of the voltage application means 18 is reversed, the polarity of the voltage applied to the inner wall voltage application means 26 is also changed. Inverted.

  Next, the flow of the volatile organic substance detection method in the present embodiment will be described. As shown in FIG. 2, first, a volatile organic substance to be measured is introduced into an ion detection chamber whose inner wall is made of a conductor, and the volatile organic substance is irradiated with UV from a UV lamp (ionization). Energy supply) and ionize volatile organics.

  By configuring the inner wall (detection chamber wall) of the ion detection chamber with a conductor, it is possible to suppress the bias of charge in the ion detection chamber and to stably measure the ion current. Subsequently, the ionized ions are detected (captured) by at least one pair of ion detection electrodes to which a predetermined voltage is applied.

  Further, a voltage lower than a predetermined voltage applied to the ion detection electrode is applied to the inner wall of the ion detection chamber. In this way, by applying a voltage lower than the predetermined voltage applied to the ion detection electrode to the inner wall of the ion detection chamber, ions that are not detected (captured) by the ion detection electrode can be obtained. It will be captured by the inner wall of the ion detection chamber.

As a result, accumulation of charged particles does not occur on the inner wall of the ion detection chamber, and most ions are prevented from moving to the inner wall (detection chamber wall) of the ion detection chamber rather than the ion detection electrode. Since the sensitivity can be maintained, the ion current can be measured more stably. Then, when ions or electrons are detected (captured) by the ion detection electrode, a current flows through the ion detection electrode, and the current value is measured by a current value measuring device.

  Next, once the current value is measured by the current value measuring device, the polarity of the voltage applied to the ion detection electrode is reversed. If it does so, the ion ionized by UV irradiation will move to the other electrode, and will be captured again. Then, since a current flows through the ion detection electrode, the value of this current is again measured by the current value measuring device. When the polarity of the voltage applied to the ion detection electrode is reversed, the polarity of the voltage applied to the inner wall of the ion detection chamber is also reversed at the same time.

  The UV irradiation range is between the ion detection electrodes and is a range biased to one of the ion detection electrodes. Therefore, the current values measured before and after inversion are different from each other. Become. Then, the calculation device for calculating the diffusion constant obtains the current ratio from the measured current values before and after inversion, calculates the diffusion constant of the volatile organic substance to be measured from the current ratio, and calculates the calculated diffusion constant. The type of volatile organic matter can be specified from the above. In addition, the type of the volatile organic substance specified by the calculated diffusion constant is displayed by a display unit provided in the calculation apparatus.

  In addition, based on the current value measured by the current value measuring device, the concentration of the volatile organic substance to be measured can also be calculated. The calculation method is, for example, toluene as described above. If so, data obtained by an experiment in advance is stored in a storage device, and calculation is performed using the data. Furthermore, for example, when the gas to be measured contains a plurality of types of volatile organic substances, the calculated diffusion constant is the average value of the plurality of types of volatile organic substances, and this average value is displayed on the display means. If it is displayed, it becomes possible to obtain useful information as a guideline for ventilation in factories and the like.

(Volatile organic substance detection theory)
Hereinafter, the theory for calculating the diffusion constant of the volatile organic substance to be measured by the volatile organic substance detector and the volatile organic substance detection method will be described in more detail.

  First, when the volatile organic material is irradiated with UV, the molecules of the volatile organic material emit electrons and become cations. On the other hand, electrons released in the air are trapped by oxygen molecules having a high electron affinity and form anions.

Here, in order to characterize the flight of positive and negative ions to the electrodes, as shown in FIG. 3, a configuration in which a UV lamp is provided at a position biased to one electrode and only a part between the electrodes is irradiated is used. . One of the ions flies in a space not irradiated with UV and reaches the electrode, so that the current flowing through the system varies depending on the ease of ion movement. Ion density n, the ion mobility μ is, the current I flowing when moving space of the cross-sectional area S by a distance d, a potential difference V, and elementary charge When e _c, to be represented by the following formula Become.

The positive ion mobility is μ ₊ , the negative ion mobility is μ ₋ , the UV irradiation distance is 2d ₁ , the UV irradiation distance is d _2, and the ion density and the cross-sectional area are the same. Then, the resistance value of FIG. 3A is expressed by the following equation.

Next, the current flowing in FIG. 3A is I ₋ , and (b) is I _+, and the ratio of the current flowing when the absolute value of the potential difference is equal is expressed by the following equation.

From the structure of FIG. 3, d ₂ > d ₁ , and from the relationship between the mobility of volatile organic substances and oxygen molecules, μ ₊ <μ ₋ , and the above equation (Equation 3) is approximated by the following equation: .

Next, the diffusion constant D is proportional to μ, and since the anion is an oxygen molecular ion in the air, if the constant and constant terms of the current ratio are C ₁ and C ₂ , then The equation is as follows.

From the above equation (Equation 5), the diffusion constant is expressed as a function of positive and negative ion currents, and the measurement substance can be estimated by obtaining this diffusion constant. Further, when a diffusion constant is used in the above equation (Equation 4), it is expressed by the following equation, and by obtaining the current ratio on the left side, it becomes possible to determine volatile organic substances based on the diffusion constant. Therefore, stabilizing the ionic current and suppressing fluctuations in I ₊ and I ₋ leads to improvement in discrimination accuracy, and the present invention makes it possible.

(Experiment 1)
Next, in the embodiment of the volatile organic substance detector and the volatile organic substance detection method according to the present invention, the inner wall when o-xylene (40 ppm on a dry air basis, flow rate 400 mL / min), which is a volatile organic substance, is detected. An experiment conducted to clarify the relationship between the applied voltage and the cation current will be described.

  FIG. 4 is a schematic diagram showing an example of the configuration when an experiment is performed using the detector in the embodiment of the volatile organic substance detector and the volatile organic substance detection method according to the present invention. A state in which ions are flying in the non-UV region, and (b) represents a state in which negative ions are flying in the non-UV region. The reference numerals are the same as those in FIG. FIG. 5 is a graph showing the detection of o-xylene (40 ppm on a dry air basis, flow rate 400 mL / min) as a volatile organic substance in the embodiment of the volatile organic substance detector and the volatile organic substance detection method according to the present invention. It is the graph which showed the experimental result of the relationship between the inner wall applied voltage at the time, and a cation current.

  As shown in FIG. 4, the volatile organic substance detector 10 used in this experiment includes a UV lamp 14 that ionizes volatile organic substances, an ion detection electrode 16 that detects ions, and an inner wall that encloses the ion detection electrode 16 ( More than the ion detection chamber 12 in which the detection chamber wall 24) is made of a conductor, the voltage application means 18 for applying a voltage to the ion detection electrode 16, the current measurement means 20 for measuring the ion current, and the voltage application means 18. The inner wall voltage applying means 26 for applying a low voltage to the detection chamber wall 24 of the ion detection chamber 12 and the means for insulating the ion detection electrode 16 from the ion detection chamber 12 are configured.

  More specifically, the voltage application means 18 and the current measurement means 20 include a microammeter (Hioki Denki Co., Ltd., DSM-8104), and the inner wall voltage application means 26 includes a voltage divider (Tokyo Electronics Circuit Co., Ltd., voltage). Voltage divider) was used. In this figure, the voltage applying means 18 is expressed so that the polarity is not reversible. However, this is for convenience, and in fact, the polarities of (a) and (b) are mutually opposite. Indicates the inverted state.

  The ion detection chamber 12 having an inner wall containing the ion detection electrode 16 made of a conductor is made of aluminum, and a UV lamp 14 for ionizing volatile organic substances is manufactured by Heraeus Co., Ltd. (PKR106-6, light emitting unit). The ion detection electrode 16 and the ion detection chamber 12 were insulated by covering a fixed portion of the ion detection electrode 16 with polyolefin. The distance between the ion detection electrodes 16 was 12 mm (non-UV region: 8 mm), and a non-UV region was provided between the ion detection electrodes 16.

  In this experiment, the gas introduced into the ion detection chamber 12 was o-xylene (40 ppm on a dry air basis, flow rate 400 mL / min), and this was used as a calibration gas adjustment device (PD-1B-, manufactured by Gastec). It was made to introduce into the ion detection chamber 12 by 2). The applied voltage by the voltage applying means 18 is -300V, and the applied voltage to the inner wall by the inner wall voltage applying means 26 is changed in the range of -2V to -300V when the positive ions fly in the non-UV region. Changes in ionic current were measured.

  The experimental results are shown in FIG. As shown in the graph, the voltage applied by the inner wall voltage applying means 26 has a maximum value of ion current in the vicinity of −60 V, and in the range of −60 V to −300 V, ions are more likely to enter the detection chamber wall 24 than the ion detection electrode 16. You can see that there is a lot of movement. Therefore, the voltage applied by the inner wall voltage application means 26 is not suitable for the absolute value greater than -60V.

(Experiment 2)
Subsequently, in the embodiment of the volatile organic substance detector and the volatile organic substance detection method according to the present invention, benzene, p-xylene (on a dry air basis) 40 ppm, and a flow rate of 400 mL / min) are detected as volatile organic substances. An experiment conducted to clarify the temporal change of the ion current ratio at the time is described.

  FIG. 6 shows detection of benzene and p-xylene (40 ppm on a dry air basis, flow rate of 400 mL / min) as volatile organic substances in the embodiment of the volatile organic substance detector and the volatile organic substance detection method according to the present invention. In the graph which showed the time change of the ion current ratio at the time of making it, (a) represents the thing by the conventional detector, (b) represents the thing by this embodiment.

  In this experiment, the volatile organic substance detector 10 used in Experiment 1 was used. The gas introduced into the ion detection chamber 12 is benzene, p-xylene (based on dry air) 40 ppm, flow rate 400 mL / min), and this is a calibration gas preparation device (manufactured by Gastec, PD-1B-2). ) To be introduced into the ion detection chamber 12. Then, the voltage applied by the voltage applying means 18 was set to ± 300 V, and negative ions or positive ions measured positive and negative ion currents when flying in the non-UV region, and the ion current ratio was obtained. The applied voltage by the inner wall voltage applying means 26 was ± 4V.

  The experimental results are shown in FIG. In the graph, “Ben” is attached to benzene as the introduced gas. The maximum value is (Max), the average value is (Ave), and the minimum value is (Min). Yes. In addition, “pXy” is attached to p-xylene as the introduced gas, and these also have a maximum value (Max), an average value (Ave), and a minimum value (Min), respectively. Represents. As shown in the graph, in the time variation of the ionic current ratio of benzene and p-xylene, the prior art (PTFE detector) shown in (a) and the volatile organic substance detector 10 in the present embodiment shown in (b). From comparison of the (aluminum ion detection chamber 12), it was found that the output of the volatile organic substance detector 10 in the present embodiment can be obtained more stably than in the prior art.

(Experiment 3)
Furthermore, in the embodiments of the volatile organic substance detector and the volatile organic substance detection method according to the present invention, benzene, o-xylene, p-xylene (40 ppm on a dry air basis, flow rate 400 mL / min) are used as volatile organic substances. An experiment for clarifying the relationship between the inner wall applied voltage (guard voltage) and the ion current ratio at the time of detecting the ion is described.

  FIG. 7 shows volatile organic substances in the embodiment of the volatile organic substance detector and the volatile organic substance detection method according to the present invention. As volatile organic substances, benzene, o-xylene, p-xylene (40 ppm on a dry air basis, flow rate 400 mL / min) ) Is a graph showing the relationship between the inner wall applied voltage (guard voltage) and the ionic current ratio.

  In this experiment, the volatile organic substance detector 10 used in Experiment 1 was used. The gas introduced into the ion detection chamber 12 is benzene, o-xylene, p-xylene (40 ppm on a dry air basis, flow rate 400 mL / min), and this is a gas adjustment device for calibration (manufactured by Gastec, PD -1B-2) is introduced into the ion detection chamber 12. Then, when the voltage (guard voltage) applied to the detection chamber wall 24 of the ion detection chamber 12 was changed in the range of 2V to 20V, the relationship between the voltage and the ion current ratio was obtained.

  The experimental results are shown in FIG. The theoretical values in the graph are obtained from the oxygen diffusion constant, the interelectrode distance, and the UV irradiation radius. The error range in the graph represents the maximum and minimum values in five experiments. And it became clear that the error range of each gas does not overlap in all the experimental points, and the target gas can be discriminated with high accuracy from the ion current ratio.

  In FIG. 7, when the inner wall applied voltage (guard voltage) is low, the error range is large, while when it is high, the difference from the theoretical value is large. From this, it can be seen that the inner wall applied voltage (guard voltage) has an optimum value in the range of 4V to 10V.

(Experiment 4)
Here, the comparison data of the current value of the cation when the detection chamber 52 shown as an example in FIG. 8 is experimented with the conventional PID manufactured by PTFE and the volatile organic substance detector in the present embodiment is shown in FIG. 9 shows. In the graph, “Al I +” is attached to the volatile organic substance detector in this embodiment, and the maximum value is (max), the average value is (a), and the minimum value is (min). It represents as. Also, “PTFE I +” is attached to the conventional PID, and these are also expressed as the maximum value (max), the average value (a), and the minimum value (min), respectively. .

  As shown in FIG. 9, it can be seen that the current value by the conventional PID is small, and the current value by the volatile organic substance detector in the present embodiment is about 0.3 nA larger on average. This is because ions are adsorbed on the inner wall of the detection chamber 52 in the conventional PID. That is, the volatile organic substance detector according to the present invention has an excellent effect that ion adsorption can be reduced as compared with a conventional PID or the like.

  According to the volatile organic substance detector and the volatile organic substance detection method of the present invention, since the inner wall of the detection chamber is a conductor, charged particles do not accumulate on the inner wall, and the bias in the detection chamber is suppressed. Moreover, a stable ion current can be measured by applying a voltage to the detection chamber wall. In addition, it is possible to determine the diffusion constant, which is an important property of volatile organic matter, as well as the concentration of volatile organic matter with a simple device and a small device. Useful for detection. Furthermore, since the type of the volatile organic substance can be specified from the size of the diffusion constant, the sensitivity of the volatile organic substance detector can be corrected based on the type of the volatile organic substance, and thus high detection accuracy is required. It will be extremely useful in the scene.

DESCRIPTION OF SYMBOLS 10 Volatile organic substance detector 12 Ion detection chamber 14 UV lamp 16 Ion detection electrode 18 Voltage application means 20 Current measurement means 22 Diffusion constant calculation means 24 Detection chamber wall 26 Inner wall voltage application means

Claims (3)

Ionization energy supply means for supplying ionization energy to the volatile organic matter in order to ionize the volatile organic matter;
At least one pair of ion detection electrodes for detecting the ionized ions;
A detection chamber containing the ion detection electrode;
Voltage application means capable of reversing the voltage polarity for applying a predetermined voltage to the ion detection electrode;
Current measuring means for measuring a current value flowing through the ion detection electrode;
A diffusion constant calculating means for calculating a diffusion constant of the volatile organic substance from a current ratio based on a current value before and after voltage polarity reversal measured by the current measuring means when the voltage polarity is reversed by the voltage applying means;
The ionization energy supply means is provided between the ion detection electrodes, and is provided so as to supply the ionization energy in a range biased to one of the ion detection electrodes. In the volatile organic matter detector where a range in which the ionization energy is not supplied occurs,
The inner wall of the detection chamber is made of a conductor, and is provided with inner wall voltage application means capable of reversing the voltage polarity for applying a voltage lower than the voltage applied to the ion detection electrode to the inner wall. Features volatile organic matter detector.   The ionization energy supply means includes a UV irradiation means for irradiating the volatile organic substance with UV, an ionizing radiation emission means for emitting ionizing radiation to the volatile organic substance, and a corona discharge to the volatile organic substance. 2. The volatile organic substance detector according to claim 1, further comprising any one of corona discharge means to be performed. An ionization step of ionizing the volatile organic substance by supplying ionization energy to the volatile organic substance flowing into the detection chamber having an inner wall made of a conductor;
An ion detection step of detecting ions ionized by the ionization step with at least one pair of ion detection electrodes to which a predetermined voltage is applied;
An inner wall voltage application step of applying a voltage lower than a predetermined voltage applied to the ion detection electrode to the inner wall;
A current value measuring step of measuring a current value flowing through the ion detection electrode;
By inverting the polarity of the voltage applied to the ion detection electrode, the current ratio is obtained from the current value flowing through the ion detection electrode before and after the inversion, and the diffusion constant of the volatile organic matter is determined from the current ratio. A diffusion constant calculating step to calculate;
In the diffusion constant calculation step, when the polarity of the voltage applied to the ion detection electrode is reversed, the inner wall voltage application reversal for determining the polarity of the voltage applied to the inner wall in the inner wall voltage application step. Process,
Including
In the ionization process, the ionization energy is supplied between the ion detection electrodes by supplying the ionization energy to a range biased to one of the ion detection electrodes. A volatile organic matter detection method characterized by causing a range not to be supplied and supplying ionization energy to the volatile organic matter.

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