JPH11118744A - Odor measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To condense a sample gas using an adsorbent deteriorated in performance subsequent to oxidation in an odor measuring apparatus using an odorant sensor of an oxide semiconductor. SOLUTION: When a sample component adsorbed to an adsorbent in a collecting tube 22 is to be sent to flow cells 28a, 28b, N2 is sent to the collecting tube 22 via a nitrogen gas path 15 and a six-way valve 21, and the collecting tube 22 is heated by a heater 23. The N2 including the sample component first passes the flow cell 28a where an odorant sensor 29a constituted of a conductive polymer is set. Thereafter, the air supplied with a predetermined pressure from a tank 34 storing the air is mixed with the N2 , and is sent through the flow cell 28b where an odorant sensor 29b of an oxide semiconductor is installed. Thereafter, O2 does not come in touch with the adsorbent when the adsorbent in the collecting tube 22 is heated, while O2 is adsorbed to the odorant sensor 29b. Accordingly the sample component can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an odor measuring device for measuring an odor component contained in a sample gas using an odor sensor which is a kind of gas sensor. The odor measuring device of the present invention is applicable to a wide range of fields such as quality inspection of foods and fragrances, quantitative detection of odor pollution, fire alarm by detection of burnt odor, and further, criminal investigation such as tracking, identification, authentication and drug testing of persons. Available to

[0002]

2. Description of the Related Art An odor sensor electrically (or optically) converts a physical change of an odor component contained in air (or a supplied sample gas) caused by adhering to a sensitive surface of the sensor. It is to be measured. As an odor sensor, a sensor using an oxide semiconductor and a sensor using a conductive polymer are known.

[0003] When an odor component in a sample gas having a relatively low concentration is measured by such an odor measurement device using an odor sensor, a thermal desorption method (thermal desorption) is used to increase the concentration of the component to be measured. ) Is often performed. In the thermal desorption method, first, a sample gas is passed through a concentrating tube filled with an adsorbent that mainly adsorbs the component to be measured, and the component to be measured contained in the sample gas is adsorbed by the adsorbent. Then, after the component to be measured is sufficiently adsorbed, the temperature of the adsorbent is rapidly raised while flowing a carrier gas through the concentrating tube. Thereby, the adsorbed component to be measured is released in a short time, and is introduced into the odor sensor at a high concentration.

[0004]

By the way, in an odor sensor using an oxide semiconductor such as tin oxide for a sensitive film,
The change in conductivity of the oxide semiconductor which occurs when the oxygen and the reducing gas adsorbed on the oxide semiconductor perform an oxidation-reduction reaction is detected. Therefore, the carrier gas for transporting the sample components must be a gas containing oxygen (for example, air). That is, in the odor measuring device 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,
As the adsorbent, one that does not deteriorate in performance even when heated to a high temperature in the presence of oxygen must be used.

[0005] Generally, the target component of the adsorbent differs depending on the type thereof. Therefore, if the type of adsorbent that can be used is limited for the above-mentioned reason, the target component is also limited. Specifically, for example, when a normal carbon-based adsorbent is heated in the presence of oxygen, the adsorbent itself is oxidized and its performance is greatly deteriorated. Therefore, it cannot be used for the concentration tube of the odor measuring device as described above.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The main objects of the present invention are to provide an odor sensor which requires oxygen to detect odor components such as an oxide semiconductor and a concentration device by a heat desorption method. Even in the case of combination, it is an object of the present invention to provide an odor measuring device capable of performing measurement on a wide range of sample components without limiting the selection of an adsorbent for concentration.

[0007]

Means for Solving the Problems To solve the above problems, the odor measuring apparatus of the present invention comprises: a) gas supply means for supplying an inert gas; and b) adsorption and heating of sample components. A) a collecting means provided with an adsorbent for releasing the sample component, c) a flow path for introducing a sample gas containing the sample component into the collecting means and then discharging the gas to the outside, and a gas supply means for supplying the sample gas. Flow path switching means for selecting and switching a flow path for introducing an inert gas into the collection means; andd) mixing oxygen or a gas containing oxygen into the inert gas passing through the collection means. Means, and e) odor detecting means for detecting a sample component contained in an inert gas in which oxygen or a gas containing oxygen is mixed in the mixing means, and allowing the sample gas to flow through the collecting means. To adsorb the sample components to the collecting means, By switching the path switching means to desorb the sample component adsorbed by the collection means into an inert gas, introducing oxygen or a gas containing oxygen into the odor detection means, and then introducing the mixture into the odor detection means. I have.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The above-mentioned inert gas is an appropriate gas as long as it is an inert gas particularly in a process in which it is necessary to avoid oxygen and does not corrode or damage the odor detecting means and the like. For example, a rare gas such as a nitrogen gas or a helium gas, or a mixed gas thereof can be used.

In the odor measuring device 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 components contained in the sample gas are adsorbed on the adsorbent. After the sample components have been sufficiently adsorbed, the flow path switching means is switched to flow nitrogen gas (or another inert gas) through the collection means. At this time, by heating the adsorbent of the collecting means, the sample component adsorbed by the adsorbent is released and released into nitrogen gas. The mixing means mixes the oxygen gas or the gas containing oxygen with the nitrogen gas containing the sample component, and sends the mixed gas to the odor detecting means. Thus, the sample component reaches the odor detection means on the carrier gas mainly composed of the nitrogen gas containing the oxygen gas. Even if the odor detection means requires oxygen in the process of detecting a sample component using an oxide semiconductor or the like, 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, there is no possibility that the adsorbent is oxidized even when the adsorbent is heated.

[0010] In the odor measuring device according to the present invention, as the odor detecting means, both a sensor that requires oxygen for detection and a sensor that uses a conductive polymer or the like that preferably avoids oxygen are used in combination. In such a case, the following configuration can be adopted. That is, the odor detection means is divided into a first detection section having a sensor that does not require oxygen for detection and a second detection section having a sensor that requires oxygen for detection, and has passed through the collection means. An inert gas is introduced into the first detection unit, and oxygen or a gas containing oxygen is mixed into the gas flowing out of the first detection unit by the mixing unit, and then is introduced into the second detection unit.

In this configuration, the sample component is introduced into the first detection unit using only nitrogen gas as a carrier gas, and the sample component is introduced into the second detection unit using a carrier gas containing oxygen gas and containing nitrogen gas as a main component. Is done. Accordingly, since oxygen gas does not flow through the first detection unit, deterioration due to oxidation can be prevented even for a sensor or the like using a conductive polymer. On the other hand, since oxygen gas flows through the second detection unit, the detection of sample components can be performed using an odor sensor or the like using an oxide semiconductor.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the odor measuring device according to the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram centering on the gas flow path of the odor measuring device of the present embodiment.

A nitrogen gas container 1 filled with pure nitrogen gas
The flow path on the outlet side of the constant-pressure valve 11 provided at the gas outlet of the first gas outlet includes flow control units 13 and 16 such as a mass flow controller and two molecular sieve filters 14 and 17 for removing impurities. And a second nitrogen gas flow path 12, 15. PTF for dust removal
Sample gas supply port 18 through E membrane filter 19
The sample gas flow path and the first nitrogen gas flow path 12 are selectively connected to a port a of a six-way valve (6-port 2-position valve) 21 by a three-way valve 20.
The second nitrogen gas flow path 15 is connected to the port d of the six-way valve 21. A collection tube 22 provided with a heater 23 for heating is connected between the port c and the port f of the six-way valve 21. The collection tube 22 is filled with, for example, a carbon-based adsorbent or another appropriate adsorbent according to the sample component to be measured.

The port b of the six-way valve 21 is selectively connected to a flow path that passes through the pump 25 and the flow meter 26 or a flow path that does not pass through the three-way valve 24, and both reach the discharge port 27. The port e of the hexagonal valve 21 is connected to a first flow cell 28a having a plurality of odor sensors 29a.
The downstream side thereof is connected to a second flow cell 28b having a plurality of odor sensors 29b, and the downstream side thereof is connected to the discharge port 31. Odor sensor 29a
Is an odor sensor using a conductive polymer having characteristics different in detection sensitivity from various sample components for a sensitive film. On the other hand, the odor sensor 29b is an odor sensor that uses an oxide semiconductor having characteristics of different detection sensitivities for various sample components as a sensitive film. The detection signals of the plurality of odor sensors 29a and 29b are
Signal processing unit 3 for performing processing such as identification and classification of odor components
Input to 0.

The air sucked from the air supply port 32 by the pump 33 is compressed and stored in a tank 34, and a third flow control unit 35 and an activated carbon filter 3 for removing impurities are used.
6 and is connected to a flow path connected from the first flow cell 28a to the second flow cell 28b. The six-way valve 21 and the entire first and second flow cells 28a and 28b are installed in a thermostat 37, and the thermostat 37 is controlled to a predetermined temperature by a temperature regulator 38.

The control unit 40 is provided with an operation unit 39, which controls the three-way valves 20, 24, the six-way valves 21, the pumps 25, 33, the heater 23, the temperature adjustment unit 38, and the like according to a predetermined program, as described later. Controlling. In addition, as a piping material of each flow path, PTF with little adsorption of sample components is used.
It is desirable to use an E tube, but in order to prevent oxygen from being mixed in the nitrogen gas as much as possible, the first nitrogen gas flow path 12 from the outlet of the nitrogen gas container 10 to the three-way valve 20 and the port of the six-way valve 21 metal pipe such as stainless steel in the second nitrogen gas flow path 15 up to d.
It is more desirable to use a stainless steel pipe or the like whose inner surface is coated with a phased silica that has been inertly treated in the flow path from the port c to the collection pipe 22.

Next, the operation of the odor measuring device 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 The three-way valve 24 is switched so as to be connected to. The connection state indicated by the broken line in FIG.
And the pump 25 is operated. Then, by the suction force of the pump 25, the sample gas sucked from the sample gas supply port 18 is subjected to removal of relatively large suspended solids such as dust by the membrane filter 19, and is captured via the three-way valve 20 and the six-way valve 21. It is introduced into the collecting pipe 22 (from left to right in FIG. 1). Further, the gas is discharged from a discharge port 27 through a six-way valve 21, a three-way valve 24, a pump 25, and a flow meter 26. The control unit 40 controls the suction force of the pump 25 so that the value detected by the flow meter 26 becomes a predetermined value.

The sample gas contains odor components to be measured in air, and the odor components are a mixture of a plurality of sample components. When the sample gas passes through the collection tube 22 as described above, heating by the heater 23 is not performed, and each sample component contained in the sample gas is adsorbed by the adsorbent.

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 flows through the six-way valve 21 to the first and second flow cells 28a and 28b. Then, it is discharged from the discharge port 31 to the outside. Thereby, the odor sensors 29a and 29b are always kept in the nitrogen gas atmosphere. At this time, the air sent from the tank 34 may be mixed into the nitrogen gas and flow into the flow cell 28b side as described later.

(Ii) Replacement of Gas in Collection Tube 22 After the sample gas has been circulated 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 of the six-way valve 21. a and a three-way valve 2
4 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 is supplied to the first nitrogen gas channel 12 -the three-way valve 20 -the six-way valve 21 -the collection pipe 22.
Through the six-way valve 21-the three-way valve 24 and the outlet 27
Is discharged from As a result, the sample gas remaining inside the flow path including the collection tube 22 is pushed out to the outside 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. In addition, since nitrogen gas is extremely dry, most of the water adsorbed by the adsorbent during the introduction of the sample gas is carried away to the outside by the nitrogen gas, thereby achieving a certain degree of dehumidification. .

(Iii) Introduction of Sample Components into Odor Sensor After nitrogen gas is allowed to flow through the collection tube 22 for a predetermined time, the six-way valve 21 is switched to the connection state shown by the solid line in FIG.
Then, the second nitrogen gas flow path 15-the hexagonal valve 21-the collection pipe 22-the hexagonal valve 21-the first flow cell 28a-the second
A flow path from the flow cell 28b to the outlet 31 is formed. In this state, the heater 23 is energized to rapidly heat the collection tube 22. As a result, the sample component adsorbed on the adsorbent in the collection tube 22 separates from the adsorbent, and rides on the nitrogen gas flowing in the opposite direction (from right to left in FIG. 1) to that before the sample component. It is carried to one flow cell 28a. Here, the volume of the nitrogen gas passing through the collecting tube 22 during the period from when the heating of the collecting tube 22 is started to when the sample component is almost completely separated from the adsorbent is reduced in the above (i). By setting each part so as to be smaller than the volume of the sample gas passing through the sample gas, the gas in which the sample component is concentrated
8a.

If the flow rate of the nitrogen gas flowing through the flow cell 28a fluctuates when the temperature of the collection tube 22 changes as described above and the flow path resistance changes, the odor sensor 29
There is a possibility that a detection error may occur in a. Flow control unit 1
For example, if a secondary pressure fluctuation type mass flow controller of a mechanical control type is used for the flow path 6, the flow rate of the nitrogen gas passing therethrough can be kept constant even if the flow path resistance of the outlet side, that is, the flow path fluctuates. In order for this mass flow controller to operate normally, a differential pressure between the inlet side pressure and the outlet side pressure needs to be maintained at a certain level or more. Therefore, the set pressure of the constant pressure valve 11, the inner diameter of the pipe, the flow rate of the air mixed through the flow control unit 35, and the like are determined so that the differential pressure can be reliably obtained. Thus, the flow rate of the nitrogen gas is accurately controlled, and the mixed gas does not flow back to the first flow cell 28a from the location where the air is mixed.

As described above, when the nitrogen gas containing the sample component passes through the first flow cell 28a, the sample component is adsorbed on 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 is reduced. Changes. The detection signals due to the resistance change are sequentially sent to the signal processing unit 30.

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 an undesired component which becomes a disturbance of the measurement is removed by the activated carbon filter 36. , First flow cell 2
It is mixed with the nitrogen gas containing the sample component passed through 8a.
Since oxygen gas is contained in air, oxygen gas flows into the second flow cell 28b together with the sample component, and oxygen gas molecules are adsorbed on the sensitive film made of an oxide semiconductor. This causes a redox reaction. As a result, the conductivity of the odor sensor 29b changes, and the electrical resistance between the electrodes changes. The detection signal due to the resistance change is also sequentially sent to the signal processing unit 30.

Since the plurality of odor sensors 29a and 29b have different characteristics, for example, a large detection signal is obtained from a certain odor sensor with respect to a certain sample component and completely different from other odor sensors. It is possible that a detection signal cannot be obtained. Therefore, the signal processing unit 30
Using the plurality of detection signals thus obtained, a predetermined multivariate analysis process such as a principal component analysis process or a hierarchical cluster analysis process is performed to comprehensively identify or classify odor components.

During the measurement of the sample components, the hexagonal valve 21, the first and second flow cells 28a and 28b, and the flow path connecting them are controlled by the temperature control unit 38 at a constant temperature higher than room temperature (for example, 40 ° C.). ° C). Thereby, the odor sensors 29a, 29b due to the fluctuation of the ambient temperature
And it is possible to prevent the high-boiling point compound from adhering to the inner wall of the flow path and the like, thereby deteriorating the stability of the detection sensitivity.

A series of processes relating to the above-described measurement can be automatically performed in accordance with a program preset in the control unit 40. For example, parameters such as the time for switching each valve and the heating temperature of the heater 23 can be used. Is
It is preferable that the setting can be appropriately made from the operation unit 39 according to the type of the sample component. In addition to the automatic measurement, a configuration may be adopted in which each measurement process is manually advanced by the measurer giving successive instructions from the operation unit 39.

In the above embodiment, the second flow cell 2
Although air is mixed in the flow path before 8b, pure oxygen gas may be mixed instead of air. If pure oxygen gas is used, the volume to be mixed can be much reduced as compared with air, so that the rate of dilution of the sample component is small, which is advantageous in improving the sensitivity of detection by the odor sensor 29b.

Further, the first or second flow cell 28a,
As the 8b, an odor sensor having another structure, such as an odor sensor in which a quartz oscillator is coated with a synthetic bilayer film, can be used. Odor sensors that do not require oxygen for detection
Installation in the first flow cell 28a located further upstream is more advantageous in terms of detection sensitivity. The reason is that, first of all, in the second flow cell 28b, the flowing gas is diluted by the mixed air, so that the concentration of the sample component becomes low. 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 directed 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 (time-wise) spread at the time of reaching is small and the concentration of the sample component is relatively high.

It should be noted that the above embodiment is merely an example, and it is apparent that modifications and modifications can be made as appropriate within the spirit of the present invention.

[0031]

As described above, in the odor measuring device according to the present invention, after the inside of the collection tube is replaced with an inert gas, heating is performed for sample separation and removal, and the collection tube and the sample are separated. Oxygen gas is mixed in the middle of a flow path connecting an odor sensor that requires oxygen to detect an oxide semiconductor or the like. Accordingly, since the oxygen gas does not come into contact with the adsorbent when the adsorbent in the collection tube is at a high temperature, an adsorbent whose performance may be deteriorated by oxidation can be used. As a result, the range of selection of the adsorbent is expanded, and the types of sample components that can be measured are increased.

In addition, an odor sensor using a conductive polymer or the like is disposed upstream of a portion where oxygen or a gas containing oxygen is mixed, and an odor sensor using an oxide semiconductor or the like is disposed downstream. According to this, it is possible to use sensors of different types, that is, a sensor that preferably avoids oxygen and a sensor that requires oxygen for detection. Therefore, the types of sample components that can be measured increase. Further, since the odor sensor on the upstream side 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. In addition, since the odor sensor on the upstream side measures the sample components on the flow path closer to the collection tube, the spread of the sample components over time is small, which is advantageous for high-sensitivity measurement.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an odor measuring device 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 unit 18 ... Sample gas supply port 20, 24 ... Three-way valve 21 ... 6-way valve 22 ... Collection tube 23 ... Heater 25, 33 ... Pump 26 ... Flow meter 27, 31 ... Outlet 28a, 28b ... Flow cell 29a ... Odor sensor (conductive polymer) 29b ... Odor sensor (oxide semiconductor) 30 ... signal processing unit 32 ... air supply port 34 ... tank 37 ... constant temperature bath 38 ... temperature adjustment unit 39 ... operation unit 40 ... control unit

Claims (1)

[Claims] 1. a) gas supply means for supplying an inert gas; b) collection means provided with an adsorbent for adsorbing a sample component and releasing the sample component by heating; A flow path for selecting and switching between a flow path for discharging a sample gas containing the gas to the collection means and then discharging the sample gas to the outside and a flow path for introducing an inert gas supplied from the gas supply means to the collection means. Switching means; d) mixing means for mixing oxygen or a gas containing oxygen into the inert gas that has passed through the collecting means; ande) inert gas containing oxygen or a gas containing oxygen in the mixing means. An odor detecting means for detecting a sample component contained in the natural gas, and allowing the sample gas to flow through the collecting means to adsorb the sample component to the collecting means, and then switching the flow switching means. The sample components adsorbed by the collection means are placed in an inert gas. An odor measuring device, wherein the odor detecting device is separated and mixed with oxygen or a gas containing oxygen and then introduced into the odor detecting means.