JP3777753B2 - Odor measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an odor measurement apparatus that measures an odor component contained in a sample gas using an odor sensor that is a kind of gas sensor. The odor measuring device of the present invention is used in a wide range of fields such as quality inspection of foods and fragrances, quantitative detection of bad odor pollution, fire alarm by detection of burnt odor, and criminal investigations such as person tracking, identification, authentication and drug inspection Is available.
[0002]
[Prior art]
The odor sensor electrically (or optically) measures a physical change of an odor component contained in air (or supplied sample gas) caused by adhering to a sensitive surface of the sensor. . As an odor sensor, one using an oxide semiconductor or one using a conductive polymer is known.
[0003]
When measuring odor components in a sample gas with a relatively low concentration using such an odor sensor, a gas by thermal desorption (thermal desorption) is used to increase the concentration of the component to be measured. Concentration treatment is often performed. In the thermal desorption method, first, a sample gas is circulated through a concentration tube filled with an adsorbent that mainly adsorbs a component to be measured, and the component to be measured contained in the sample gas is adsorbed to the adsorbent. Then, after the component to be measured is sufficiently adsorbed, the temperature of the adsorbent is rapidly raised while flowing the carrier gas through the concentration tube. As a result, the component to be measured that has been adsorbed is released in a short time, and is introduced into the odor sensor at a high concentration.
[0004]
[Problems to be solved by the invention]
By the way, in an odor sensor that uses an oxide semiconductor such as tin oxide as a sensitive film, the change in conductivity of the oxide semiconductor that occurs when oxygen and reducing gas adsorbed on the oxide semiconductor undergo a redox reaction. Detected. For this reason, the carrier gas for transporting the sample components must be a gas containing oxygen (for example, air). That is, in the odor measuring apparatus using the concentration tube as described above, the gas containing oxygen flows through the concentration tube while the adsorbent in the concentration tube is heated to a high temperature. Therefore, an adsorbent that does not deteriorate in performance even when heated to a high temperature in the presence of oxygen must be used.
[0005]
In general, since the target component differs depending on the type of the adsorbent, if the type of adsorbent that can be used is limited for the above reason, the target component is also limited. Specifically, for example, when an ordinary carbon-based adsorbent is heated in the presence of oxygen, the adsorbent itself is oxidized and the performance is greatly deteriorated. For this reason, it cannot be used for the concentration tube of the odor measuring apparatus as described above.
[0006]
The present invention has been made to solve the above-mentioned problems, and its main purpose is to combine an odor sensor that requires oxygen to detect an odor component, such as an oxide semiconductor, and a concentrator using a thermal desorption method. However, the selection of the adsorbent for concentration is not limited, and an object is to provide an odor measuring apparatus capable of performing measurement on a wide range of sample components.
[0007]
[Means for Solving the Problems]
The odor measuring apparatus of the present invention made to solve the above problems is
a) a gas supply means for supplying an inert gas;
b) a collecting means provided with an adsorbent that adsorbs the sample components and releases the sample components by heating;
c) Select a flow path for introducing a sample gas containing a sample component to the collection means and then discharging the gas to the outside, and a flow path for introducing an inert gas supplied from the gas supply means to the collection means. Flow path switching means for switching,
d) mixing means for mixing oxygen or a gas containing oxygen into the inert gas that has passed through the collecting means;
e) at least a sensor that requires oxygen to detect odor components, and odor detection means for detecting a sample component contained in an inert gas mixed with oxygen or a gas containing oxygen by the mixing means;
A sample gas is circulated through the collecting means to adsorb the sample component to the collecting means, and then the flow path switching means is switched to inactivate the sample component adsorbed on the collecting means. It is characterized by being introduced into the odor detecting means after being separated into gas and mixed with oxygen or a gas containing oxygen.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The inert gas may be an appropriate gas as long as it is an inert gas in a process that needs to avoid oxygen and does not corrode or damage the odor detecting means. A rare gas such as nitrogen gas or helium gas, or a mixed gas thereof can be used.
[0009]
In the odor measuring apparatus according to the present invention, first, the flow path switching means is switched so that the sample gas flows through the collecting means. In the collecting means, the sample component contained in the sample gas is adsorbed by the adsorbent. After the sample components are sufficiently adsorbed, the flow path switching means is switched and nitrogen gas (or other inert gas) is passed through the collection means. At this time, by heating the adsorbent of the collecting means, the sample component adsorbed on the adsorbent is released and released into the nitrogen gas. The mixing means mixes the nitrogen gas containing the sample component with oxygen gas or a gas containing oxygen, and sends the mixed gas to the odor detection means. As a result, the sample component reaches the odor detection means on the carrier gas mainly composed of nitrogen gas containing oxygen gas. Even if the odor detecting means uses an oxide semiconductor or the like and requires oxygen in the process of detecting the sample component, the sample component can be detected because the carrier gas contains oxygen. . On the other hand, since oxygen gas does not flow through the collecting means, the adsorbent is not oxidized even when the adsorbent is heated.
[0010]
Further, in the odor measuring apparatus according to the present invention, when both a sensor requiring oxygen for detection and a sensor using a conductive polymer that preferably avoids oxygen are used as odor detecting means. The following configuration can be adopted. That is, the odor detection means is divided into a first detection section provided with a sensor that does not require oxygen for detection and a second detection section provided with a sensor that requires oxygen for detection, and passed through the collection means. An inert gas is introduced into the first detection unit, and oxygen or oxygen-containing gas is mixed into the gas flowing out from the first detection unit by the mixing unit and then introduced into the second detection unit.
[0011]
In this configuration, sample components are introduced into the first detection unit using only nitrogen gas as a carrier gas, and sample components are introduced into the second detection unit using a carrier gas containing oxygen gas and containing nitrogen gas as a main component. Accordingly, since oxygen gas does not flow through the first detection unit, it is possible to prevent deterioration due to oxidation even for a sensor using a conductive polymer. On the other hand, since oxygen gas flows through the second detection unit, the sample component can be detected using an odor sensor using an oxide semiconductor.
[0012]
【Example】
Hereinafter, an embodiment of an odor measuring apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram centering on a gas flow path of the odor measuring apparatus of the present embodiment.
[0013]
The flow paths on the outlet side of the constant pressure valve 11 provided at the gas outlet of the nitrogen gas container 10 filled with pure nitrogen gas are respectively flow control units 13 and 16 such as a mass flow controller and a molecular sieve filter 14 for removing impurities. , 17 are branched into two first and second nitrogen gas flow paths 12, 15. The sample gas flow path connected to the sample gas supply port 18 via the PTFE membrane filter 19 for dust removal and the first nitrogen gas flow path 12 are selectively selected from a six-way valve (6-port two-position valve) by a three-way valve 20. 21 is connected to port a. The second nitrogen gas flow path 15 is connected to the port d of the six-way valve 21. A collecting tube 22 provided with a heater 23 for heating is connected between the port c and the port f of the hexagonal valve 21. The collection tube 22 is filled with, for example, a carbon-based adsorbent or other appropriate adsorbent according to the sample component to be measured.
[0014]
The port b of the six-way valve 21 is selectively connected by a three-way valve 24 to a flow path that passes through the pump 25 and the flow meter 26 or a flow path that does not pass through, and both reach the discharge port 27. The port e of the hexagonal valve 21 is connected to a first flow cell 28a including a plurality of odor sensors 29a, a downstream side thereof is connected to a second flow cell 28b including a plurality of odor sensors 29b, and a further downstream side thereof is a discharge port 31. It is connected to. The odor sensor 29a is an odor sensor that uses, as a sensitive film, a conductive polymer having different detection sensitivities for various sample components. On the other hand, the odor sensor 29b is an odor sensor that uses an oxide semiconductor having different detection sensitivities for various sample components as a sensitive film. Detection signals from the plurality of odor sensors 29a and 29b are input to a signal processing unit 30 that performs processing such as identification and classification of odor components.
[0015]
The air sucked from the air supply port 32 by the pump 33 is compressed and stored in the tank 34, and the second flow from the first flow cell 28a through the third flow rate control unit 35 and the activated carbon filter 36 for removing impurities. It is connected to a flow path that continues to the flow cell 28b. In addition, the entire hexagonal valve 21 and the first and second flow cells 28 a and 28 b are installed in a thermostatic chamber 37, and the thermostatic chamber 37 is controlled to a predetermined temperature by a temperature adjusting unit 38.
[0016]
The control unit 40 is provided with an operation unit 39, which controls the three-way valve 20, 24, the six-way valve 21, the pumps 25, 33, the heater 23, the temperature adjustment unit 38, etc. according to a predetermined program as will be described later. Yes. Although it is desirable to use a PTFE tube with little sample component adsorption as the piping material for each flow path, in order to prevent oxygen from being mixed in the nitrogen gas as much as possible, a three-way valve is provided from the outlet of the nitrogen gas container 10. Stainless steel metal pipes are connected to the first nitrogen gas flow path 12 up to 20 and the second nitrogen gas flow path 15 to the port d of the hexagonal valve 21, and the flow from the port c of the hexagonal valve 21 to the collection pipe 22 It is further desirable to use a stainless steel tube whose inner surface is coated with phased silica that has been inertly treated in the path.
[0017]
Next, the operation of the odor measuring apparatus will be described in detail.
(I) Collection of sample components First, the control unit 40 switches the three-way valve 20 so that the sample gas supply port 18 and the port a of the six-way valve 21 are connected, and the port b of the six-way valve 21 is connected to the pump 25. The three-way valve 24 is switched so as to be connected. In addition, the hexagonal valve 21 is switched to the connection state indicated by the broken line in FIG. Then, the sample gas sucked from the sample gas supply port 18 is removed by the membrane filter 19 by the suction force of the pump 25, and a relatively large solid suspended matter such as dust is removed, and is trapped via the three-way valve 20 and the six-way valve 21. It is introduced into the collecting tube 22 (from left to right in FIG. 1). Further, the gas is discharged from the discharge port 27 through the six-way valve 21, the three-way valve 24, the pump 25, and the flow meter 26. The control unit 40 controls the suction force of the pump 25 so that the detection value by the flow meter 26 becomes a predetermined value.
[0018]
The sample gas contains odor components to be measured in air, and this odor component is a mixture of a plurality of sample components. As described above, when the sample gas passes through the collection tube 22, heating by the heater 23 is not performed, and each sample component contained in the sample gas is adsorbed by the adsorbent.
[0019]
On the other hand, since the gas pressure at the gas outlet of the nitrogen gas container 10 is high, the nitrogen gas supplied through the second nitrogen gas flow path 15 circulates to the first and second flow cells 28a and 28b via the hexagonal valve 21 and is discharged. It is discharged from the outlet 31 to the outside. As a result, the odor sensors 29a and 29b are always held in a nitrogen gas atmosphere. At this time, on the flow cell 28b side, air sent from the tank 34 may be mixed and flowed into the nitrogen gas as will be described later.
[0020]
(Ii) Gas replacement in the collection tube 22 After passing the sample gas through the collection tube 22 for a predetermined time, the three-way valve 20 is switched to connect the first nitrogen gas flow path 12 to the port a of the six-way valve 21. At the same time, the three-way valve 24 is switched to connect the port b of the six-way valve 21 directly to the discharge port 27. Then, instead of the sample gas, the nitrogen gas supplied from the nitrogen gas container 10 passes through the first nitrogen gas flow path 12-the three-way valve 20-the six-way valve 21-the collection tube 22-the six-way valve 21-the three-way valve 24. The gas is discharged from the discharge port 27. Thereby, the sample gas remaining inside the flow path including the collection tube 22 is pushed out by the nitrogen gas. At this time, since the collection tube 22 is maintained at substantially normal temperature, the sample component previously adsorbed by the adsorbent remains as it is. Also, since the nitrogen gas is extremely dry, most of the moisture adsorbed by the adsorbent when the sample gas is introduced is carried outside by the nitrogen gas, thereby achieving dehumidification to a certain extent. .
[0021]
(Iii) Introducing the sample component into the odor sensor After flowing nitrogen gas through the collection tube 22 for a predetermined time, the hexagonal valve 21 is switched to the connected state shown by the solid line in FIG. Then, a second nitrogen gas flow path 15-a six-way valve 21-a collecting pipe 22-a six-way valve 21-a first flow cell 28a-a second flow cell 28b-a discharge port 31 is formed. In this state, the heater 23 is energized to heat the collection tube 22 rapidly. As a result, the sample component adsorbed on the adsorbent in the collection tube 22 is detached from the adsorbent, and the first component rides on the nitrogen gas flowing in the opposite direction (right to left in FIG. 1). It is carried to one flow cell 28a. Here, after the heating of the collection tube 22 is started, the volume of the nitrogen gas passing through the collection tube 22 during the period until the sample component is almost detached from the adsorbent is the collection tube 22 in the above (i). By setting each part so as to be smaller than the volume of the sample gas passing through the gas, the gas in which the sample component is concentrated can be introduced into the flow cell 28a.
[0022]
As described above, when the temperature of the collection tube 22 changes, and the flow rate resistance changes accordingly, the flow rate of the nitrogen gas flowing in the flow cell 28a may fluctuate, which may cause a detection error in the odor sensor 29a. If, for example, a mechanically controlled secondary pressure fluctuation type mass flow controller is used for the flow rate control unit 16, the flow rate of the passing nitrogen gas can be kept constant even when the outlet side, that is, the flow path resistance of the flow path fluctuates. In order for this mass flow controller to operate normally, it is necessary to ensure a certain pressure difference between the inlet side pressure and the outlet side pressure. Therefore, the set pressure of the constant pressure valve 11, the inner diameter of the pipe line, the flow rate of air mixed in via the flow rate control unit 35, etc. are determined so that this differential pressure can be obtained reliably. As a result, the flow rate of the nitrogen gas is accurately controlled, and the mixed gas does not flow backward from the location where air is mixed into the first flow cell 28a.
[0023]
When nitrogen gas containing the sample component passes through the first flow cell 28a in this manner, the sample component is adsorbed to the sensitive film made of the conductive polymer of the odor sensor 29a, and the electric resistance between the electrodes of the odor sensor 29a changes. . Detection signals due to this resistance change are sequentially sent to the signal processing unit 30.
[0024]
The air pressurized by the pump 33 and stored in the tank 34 is adjusted to an appropriate flow rate by the flow rate control unit 35, and after the undesired components that cause measurement disturbance are removed by the activated carbon filter 36, the first It is mixed in nitrogen gas containing the sample components that have passed through the flow cell 28a. Since the oxygen gas is contained in the air, the oxygen gas flows into the second flow cell 28b together with the sample component, and the oxygen gas molecules are adsorbed on the sensitive film made of the oxide semiconductor, and between the sample component molecules. Causes a redox reaction. As a result, the conductivity of the odor sensor 29b changes, and the electrical resistance between the electrodes changes. Detection signals due to this resistance change are also sequentially sent to the signal processing unit 30.
[0025]
Since the plurality of odor sensors 29a and 29b have different characteristics, for example, a large detection signal can be obtained from a certain odor sensor for a certain sample component, and no detection signal can be obtained from other odor sensors. It may be impossible to obtain. Therefore, the signal processing unit 30 performs predetermined multivariate analysis processing such as principal component analysis and hierarchical cluster analysis processing using the plurality of detection signals obtained in this manner, and comprehensively identifies odor components. Or classify.
[0026]
During the measurement of the sample components, the six-way valve 21, the first and second flow cells 28a, 28b and the flow path connecting them are kept at a constant temperature (for example, 40 ° C.) higher than room temperature by the temperature adjustment unit 38. Maintained. As a result, it is possible to reduce the influence of the odor sensors 29a and 29b due to fluctuations in the ambient temperature, and to prevent the high-boiling-point compound from adhering to the inner wall of the flow path and the like and the stability of detection sensitivity from being impaired.
[0027]
Note that a series of processes relating to the measurement as described above can be automatically performed according to a program set in advance in the control unit 40. For example, parameters such as the time for switching each valve and the heating temperature of the heater 23 may be It is preferable that the operation unit 39 can be set as appropriate according to the type of component. Further, not only automatic measurement but also a configuration in which each measurement process is manually advanced by a measurement person sequentially giving instructions from the operation unit 39.
[0028]
Moreover, in the said Example, although air was mixed in the flow path before the 2nd flow cell 28b, it is good also as a structure which replaces with air and mixes pure oxygen gas. If pure oxygen gas is used, the volume to be mixed can be greatly reduced as compared with air. Therefore, the proportion of the sample component diluted is small, which is advantageous in improving the sensitivity of detection by the odor sensor 29b.
[0029]
The first or second flow cell 28a, 28b may be an odor sensor having another structure such as an odor sensor in which a synthetic bilayer film is coated on a quartz crystal resonator. An odor sensor that does not require oxygen for detection is more advantageous in terms of detection sensitivity if it is installed in the first flow cell 28a located on the upstream side. This is because, first of all, in the second flow cell 28b, the flow gas is diluted by the mixed air, and the concentration of the sample component is lowered. Secondly, since the first flow cell 28a is located closer to the collection tube 22 on the flow path, the first flow cell 28a is in the direction along the flow path of the sample component while the gas containing the sample component flows (that is, the odor sensor). This is because the sample component concentration is relatively high and the sample component concentration is relatively high.
[0030]
It should be noted that the above embodiment is merely an example, and it is obvious that modifications and corrections can be made as appropriate within the scope of the present invention.
[0031]
【The invention's effect】
As described above, in the odor measuring apparatus according to the present invention, after the inside of the collection tube is replaced with an inert gas, heating is performed for detachment of the sample components, and the collection tube and the oxide semiconductor, etc. Oxygen gas is mixed in the middle of the flow path connecting the odor sensor that requires oxygen for detection. Therefore, since the oxygen gas does not contact the adsorbent when the adsorbent in the collection tube is at a high temperature, an adsorbent that may deteriorate in performance due to oxidation can also be used. Thereby, the selection range of the adsorbent is widened, and the types of sample components that can be measured are increased.
[0032]
In addition, according to the configuration in which an odor sensor using a conductive polymer or the like is arranged on the upstream side of the location where oxygen or oxygen-containing gas is mixed, and an odor sensor using an oxide semiconductor or the like is arranged on the downstream side, Different types of sensors can be used in combination, a sensor that preferably avoids oxygen and a sensor that requires oxygen for detection. This increases the types of sample components that can be measured. In addition, since the upstream odor sensor measures the sample component before being diluted with oxygen or a gas containing oxygen, the concentration of the sample component is high and high-sensitivity measurement is possible. Further, since the odor sensor on the upstream side measures the sample component on the flow path closer to the collection tube, the sample component is less spread over time, which is advantageous for highly sensitive measurement.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an odor measuring apparatus according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Nitrogen gas container 11 ... Constant pressure valve 12, 15 ... Nitrogen gas flow path 13, 16, 35 ... Flow control part 18 ... Sample gas supply port 20, 24 ... Three-way valve 21 ... Six-way valve 22 ... Collection tube 23 ... Heater 25, 33 ... Pump 26 ... Flow meter 27, 31 ... Discharge port 28a, 28b ... Flow cell 29a ... Odor sensor (conductive polymer)
29b ... Odor sensor (oxide semiconductor)
DESCRIPTION OF SYMBOLS 30 ... Signal processing part 32 ... Air supply port 34 ... Tank 37 ... Constant temperature bath 38 ... Temperature adjustment part 39 ... Operation part 40 ... Control part

Claims (1)

a) a gas supply means for supplying an inert gas;
b) a collecting means provided with an adsorbent that adsorbs the sample components and releases the sample components by heating;
c) Select a flow path for discharging a sample gas containing a sample component to the outside after being introduced into the collection means, and a flow path for introducing an inert gas supplied from the gas supply means to the collection means. Flow path switching means for switching,
d) mixing means for mixing oxygen or oxygen-containing gas into the inert gas that has passed through the collecting means;
e) at least a sensor that requires oxygen to detect odor components, and odor detection means for detecting a sample component contained in an inert gas mixed with oxygen or a gas containing oxygen by the mixing means;
A sample gas is circulated through the collecting means to adsorb the sample component to the collecting means, and then the flow path switching means is switched to inactivate the sample component adsorbed on the collecting means. An odor measuring apparatus which is introduced into the odor detecting means after being separated into gas and mixed with oxygen or a gas containing oxygen.

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