JP2006250890A - Volatile organic matter sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a volatile organic matter sensor having high sensitivity, low in cost, and enhanced in precision. <P>SOLUTION: The volatile organic matter sensor comprises an index substance changed to a second state from a first state by the contact with a predetermined volatile organic matter, a temperature control part for controlling the temperature of the index substance, a first light emitting device for irradiating the index substance with light of a first wavelength, a second light emitting device for irradiating the index substance with light of a second wavelength different from the first wavelength, a light detecting device for detecting the reflected light or transmitted light from the index substance to output an electric signal and a control part observing the first electric signal, which is output by irradiating the index substance with the light of the first wavelength from the first light emitting device and detecting the reflected light or transmitted light from the index substance by the light detecting device, and the second electric signal, which is outputted by irradiating the index substance with the light of the second wavelength from the second light emitting device and detecting the reflected light or transmitted light from the index substance by the second light emitting device, to discriminate the state of the index substance on the basis of the first and second electric signals to evaluate the presence of the volatile organic matter in a gas to be evaluated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a volatile organic substance sensor that detects volatile organic substances in a gas.

  In a conventional volatile organic substance (VOC) sensor, white paper is irradiated with white light to evaluate the color change of a test paper coated with a substance that changes its absorption spectrum by reacting with a chemical substance whose concentration is measured in gas. In some cases, the reflected light is received by a light receiving device of three colors, for example, a CCD or a photodiode, and the color change of the test paper is evaluated (for example, see Non-Patent Document 1).

Annual Conference of the Institute of Electrical Engineers of Japan, 2003, 3-111

  In such a volatile organic sensor, since a plurality of expensive photomultiplier tubes, CCDs, and photodiodes are used as the light receiving device, the volatile organic sensor itself is also expensive. The meaning of “expensive” includes a current evaluation circuit and a voltage evaluation circuit for measuring the device output voltage or current.

  An object of the present invention is to provide a low-cost volatile organic sensor.

The volatile organic substance sensor according to the present invention includes an indicator substance that changes from a first state to a second state by contact with a predetermined volatile organic substance,
A temperature control unit for controlling the temperature of the indicator substance;
A first light emitting device for irradiating the indicator substance with light of a first wavelength;
A second light emitting device for irradiating the indicator substance with light having a second wavelength different from the first wavelength;
A light receiving device that receives reflected light or transmitted light from the indicator substance and outputs an electrical signal; and
Irradiating the indicator substance with light of the first wavelength from the first light emitting device, observing a first electric signal output by receiving reflected or transmitted light from the indicator substance with the light receiving device, and Irradiating the indicator substance with light of the second wavelength from a second light emitting device, observing a second electrical signal output by receiving reflected or transmitted light from the indicator substance with the light receiving device, Based on one electric signal and the second electric signal, it is determined whether the indicator substance is in the first state or the second state, and the presence or absence of the volatile organic substance in the gas to be evaluated is evaluated. And a control unit.

  According to the volatile organic sensor according to the present invention, while maintaining the indicator substance at a predetermined temperature, two light emitting devices having different emission center wavelengths are sequentially emitted to irradiate the indicator substance, and reflected light from the indicator substance or Determining whether the indicator substance is in the first state or the second state based on the first electric signal and the second electric signal obtained by sequentially receiving the transmitted light with one light receiving device; The presence or absence of volatile organic substances can be evaluated stably and accurately. Thereby, a low-cost and highly accurate volatile organic substance sensor can be provided.

  A volatile organic substance sensor according to an embodiment of the present invention will be described below with reference to the accompanying drawings. In the drawings, substantially the same members are denoted by the same reference numerals.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing a configuration of a volatile organic substance sensor 10 according to Embodiment 1 of the present invention. The volatile organic sensor 10 includes seven light emitting devices 1a, 1b, 1c, 1d, 1e, 1f, and 1g each having seven light emitting diodes having different emission center wavelengths and one light receiving device 2. A diode, Nile red as the indicator substance 3, a measurement cell 6 for storing the indicator substance 3, a pipe 5 for introducing the gas to be evaluated to the measurement cell 6, a pump 4 for introducing the gas, and a measurement cell 6 includes a temperature control unit 7 that controls the index substance 3 in 6 to a predetermined set temperature, a positioning jig 8, and a control unit 9. FIG. 2 is a schematic plan view showing the positional relationship between seven light emitting devices and one light receiving device. The seven light emitting devices are arranged in an arc shape centered on one light receiving device 2. The measurement cell 6 is made of transparent glass. The light emitting diodes, which are the light emitting device and the light receiving device, are all arranged outside the measuring cell 6, but light from each light emitting device 1a, 1b, 1c, 1d, 1e, 1f, 1g passes through the measuring cell 6. The light is transmitted, partially reflected by the indicator substance 3, and reaches the light receiving device 2. The positioning jig 8 changes or fixes the relative position of each light emitting device and light receiving device 2 and the indicator substance 3. The control unit 9 controls the light emission timing of each light emitting device, and from the output of the light receiving device 2, whether the indicator material 3 is in a state before being exposed to a volatile organic substance or in a state after being exposed. And whether or not the volatile organic substance is contained in the gas to be evaluated is evaluated.

  FIG. 3 is a diagram showing the molecular formula of Nile Red of the indicator substance 3. Nile red changes color slightly by interacting with volatile organic matter (VOC) such as triethylamine. FIG. 4 shows the spectrum of triethylamine contacted with Nile Red and dilute triethylamine. Although it is difficult to understand from the graph, the absorption peak was in the vicinity of the wavelength of 510 nm before the reaction with triethylamine, but after the reaction, it slightly shifted to the short wavelength side (that is, moved to the left in the figure). As a result, the absorbance on the shorter wavelength side than the wavelength of 500 nm was slightly increased, and the absorbance on the longer wavelength side was slightly increased. As light emitting diodes used for the light emitting devices 1a, 1b, 1c, 1d, 1e, 1f, 1g, the emission center wavelengths are 405 nm (purple), 470 nm (blue), 570 nm (green), 595 nm (yellow), 630 nm (orange), Seven light emitting diodes of 640 nm (red) and 880 nm (infrared) were selected. As the light emitting diode used for the light receiving device 2, any light emitting diode having a wavelength equal to or longer than the emission center wavelength of each light emitting device can be used. For the light receiving device 2, a light emitting diode having an emission center wavelength of 960 nm was used.

  In the volatile organic sensor 10, light emitting diodes are used not only for the light emitting devices 1a, 1b, 1c, 1d, 1e, 1f, and 1g but also for the light receiving device 2. Thereby, the procurement cost of the light emitting device and the light receiving device, the mounting cost to the substrate, and the like can be reduced, and the power consumption can be reduced. Further, since the light receiving device is highly sensitive, the light emission amount of the light emitting device can be reduced, and the light deterioration of the indicator substance can be reduced.

  Note that the light-emitting device is not limited to the light-emitting diode, and an electroluminescence element may be used. The light receiving device is not limited to the light emitting diode, and a photodiode may be used.

Below, evaluation of the volatile organic substance by this volatile organic substance sensor 10 is demonstrated.
(A) First, Nile Red of the indicator substance 3 is dissolved in chloroform as a solvent so that the concentration becomes 0.5 mg / ml, and the solution is dropped on a silica plate and spread to a diameter of about 2 cm. Air dried to obtain a purple spot. The silica plate containing the spot-like indicator substance 3 was placed on the temperature control unit 7 in the measurement cell 6.
(B) Next, 2-propanol, acetaldehyde, triethylamine, and acetic acid are used as volatile organic substances to be evaluated, and the above volatile organic substances are separately provided in the air at concentrations of 250 ppm and 500 ppm as reference sample gases. I prepared something to include.
(C) The light emitting devices 1a, 1b, 1c, 1d, 1e, 1f, and 1g are arranged around the light receiving device 2 as shown in the plan view of FIG. Is fixed by the positioning jig 8.
(D) The reference sample gas was introduced into the measurement cell 6 through the pipe 5 by the pump 4 while the temperature of the indicator substance 3 was controlled to approximately 25 ° C. by the temperature controller 7.
(E) The light emitting diodes of the light emitting devices 1a, 1b, 1c, 1d, 1e, 1f, and 1g are sequentially emitted with a time interval, and the reflected light from the indicator substance 3 is received by the light receiving device 2 and output. The electrical signal was measured sequentially.
(F) Regarding the result of the output of the light receiving device 2 corresponding to each of the light emitting devices 1a, 1b, 1c, 1d, 1e, 1f, and 1g, the concentration of each volatile organic substance in the air in the reference sample gas is 250 ppm. Table 1 shows the evaluation results (response change before and after exposure (%)). Table 2 shows the evaluation results (response change (%) before and after exposure) when the concentration of each volatile organic substance in the air is 500 ppm. From this result, it can be seen that each volatile organic substance has a unique combination of responses by seven light emitting devices.
(G) Therefore, for the gas containing the volatile organic substance to be evaluated, a combination of responses from the seven light emitting devices is obtained and compared with each of the above four volatile organic substance combinations. It can be evaluated whether it is a mixture thereof. Furthermore, each concentration of the four volatile organic substances contained in the gas to be evaluated can be evaluated.

  FIG. 5 is a bar graph showing the change in response (%) before and after exposure when the gas concentration in the air in Table 1 is 250 ppm. As can be seen from this graph, the response changes before and after exposure to the four volatile organics are quite different. In addition, referring to Tables 1 and 2, it can be seen that the degree of response change depends on the concentration of volatile organic substances. That is, by using this volatile organic substance sensor, qualitative evaluation and quantitative evaluation of the volatile organic substance can be performed at low cost.

  When the temperature control of the indicator substance 3 is not performed as in the prior art, the temperature of the indicator substance 3 fluctuates depending on the temperature of the air to be introduced, so that the output value fluctuates, and from the output value from the light receiving device 2 It was difficult to estimate the concentration of volatile organics. The volatile organic substance sensor 10 includes a temperature control unit 7 that maintains the index substance 3 at a predetermined temperature. Therefore, the volatile organic substance can be accurately evaluated by the volatile organic substance sensor. In addition, when the temperature of the indicator substance 3 was raised, the time for obtaining stable data was shortened, but the response amount to the concentration was small.

  In the volatile organic sensor 10, a humidity control unit such as a humidifier that humidifies the sample gas or a dehumidifier that performs dehumidification may be further provided. In this case, when the index substance 3 is sensitive to water molecules, the influence of water molecules can be reduced. The humidifier can be a water molecule permeable membrane, a water bubbling device, etc., and the dehumidifier can be a cooling tube, a desiccant (calcium oxide etc.) filled tube, or the like.

  In addition, since said volatile organic substance is also a malodor substance, this volatile organic substance sensor can be used as a malodor sensor. In that case, since there is a subjective aspect that the smell is different for each individual, the relationship between the concentration of the volatile organic substance and the odor intensity is stored in advance as a database in the memory in the volatile organic substance sensor. May be. Alternatively, the database may be stored in an external device and acquired as necessary. By comparing the evaluation value of the volatile organic substance sensor with the database, the sensor can be used as a malodor sensor that objectively evaluates the malodor degree.

  The above four volatile organic substances (2-propanol, acetaldehyde, triethylamine, acetic acid) are malodorous substances such as alcohols (butanol etc.), aldehydes (formaldehyde etc.), amines, organic acids (butyric acid etc.) However, the present invention is not limited to these examples. This volatile organic substance sensor can also be used for evaluation of malodorous substances other than the above four substances.

  In addition, as an output evaluation circuit of the light emitting diode of the light receiving device 2, the method shown in TALANTA, Vol. 63, Issue 1, pp. 167 to 173, May 2004 can be used. This method will be described below. First, a bias reverse to that during light emission is applied to the light emitting diode as the light receiving device 2. Thereby, electric charges are accumulated in the two electrodes sandwiching the semiconductor of the light emitting part, and the light emitting diode functions as a capacitor. When the semiconductor is irradiated with light, the electric charge accumulated through the semiconductor moves and decreases because it has a resistance value corresponding to the received light intensity. As a result, the voltage between the two electrodes decreases. For example, 5 V is first applied as a reverse bias, and then a time (decay time) until the voltage is reduced to a certain voltage, for example, 1.7 V is measured. This decay time depends on the resistance of the semiconductor, that is, the received light intensity. Therefore, the received light intensity can be quantitatively obtained by measuring the decay time.

Embodiment 2
Compared with the volatile organic substance sensor according to Embodiment 1, the volatile organic substance sensor according to Embodiment 2 of the present invention is replaced with Nile Red as the indicator substance 3, methyl red, Reichart dye, or cobalt porphyrin, The difference is that a metal complex such as iron porphyrin is used. For the indicator substance 3, 5,10,15,20-tetrakis (pentafluorophenyl) 21H, 23H-porphyrin iron (III) is used. This is abbreviated as Fe (TPFP). The spot of the indicator substance 3 can be prepared in the same manner as Nile red. FIG. 6 shows the results of evaluating a sample gas containing triethylamine and acetic acid as volatile organic substances by the same method as in the first embodiment. As shown in the graph of FIG. 6, this volatile organic substance sensor can distinguish triethylamine and acetic acid, which are volatile organic substances.

Embodiment 3 FIG.
It can be considered that the volatile organic sensor according to Embodiment 3 of the present invention includes substantially two sets of the organic sensor according to Embodiment 1. In this volatile organic sensor, two indicator substances are used. The first indicator substance is Nile Red, which is the indicator substance of Embodiment 1, and the indicator substance Fe (TPFP) of Embodiment 2 is used as the second indicator substance. As the odorous substance (volatile organic substance), air mixed with 250 ppm of acetic acid or 2-propanol or triethylamine is used.

  When this volatile organic substance sensor was used to perform the same experiment as in the first embodiment, triethylamine and the other two substances could be identified by the first indicator substance Nile Red, and by the second indicator substance Fe (TPFP), Acetic acid and the other two substances could be distinguished from each other. Therefore, from the results of both the first indicator substance Nile Red and the second indicator substance Fe (TPFP), three substances, acetic acid, 2-propanol and triethylamine, could be identified. In addition, the malodor degree can be accurately determined using the evaluation data obtained by using two or more kinds of indicator substances in this way.

  In the volatile organic sensor according to each of the above embodiments, a light emitting diode is used as a light emitting device, but the present invention is not limited to this. For example, as a light emitting device, a combination of a device that emits light in a wide wavelength range, for example, white light such as a white LED, an incandescent lamp, and a fluorescent lamp, and a bandpass filter that passes only light in a predetermined wavelength range. It may be used. In this way, by combining a device that emits white light as a light emitting device and a bandpass filter, a light emitting device having a desired emission center wavelength can be easily configured. Note that one white light emitting device that emits white light, a shutter, and a band pass filter may be combined. In this case, the light emitting devices can sequentially emit light by sequentially opening and closing the shutters. Thereby, the light-emitting device which has a desired light emission center wavelength can be comprised easily.

  Moreover, in the above embodiment, the volatile organic substance sensor according to the present invention may include a memory for storing conversion data between output and concentration, and an arithmetic processing unit for conversion. Furthermore, the data for conversion may be acquired by communication from an external storage device that stores the data for conversion, or communication means such as a transmitter or an antenna for sending the calculation result to the outside may be further provided. Furthermore, the volatile organic substance sensor may include a power source such as a dry battery, a storage battery, and a solar battery, and a display device that displays data and calculation results. Further, if necessary, an alarm device for alarming based on the calculation result, and a key for inputting an alarm set value to the alarm device may be provided.

It is the schematic which shows the volatile organic substance sensor by Embodiment 1 of this invention. It is a schematic plan view which shows the positional relationship of the light emitting device and light receiving device of FIG. It is a chemical structural formula of Nile Red which is an indicator substance used in the volatile organic substance sensor according to Embodiment 1 of the present invention. It is a figure which shows the spectrum and spectrum change of the parameter | index substance used for the volatile organic substance sensor by Embodiment 1 of this invention. It is a graph which shows the result of Table 1 in Embodiment 1 of this invention. It is a graph which shows the result in Embodiment 2 of this invention.

Explanation of symbols

1a, 1b, 1c, 1d, 1e, 1f, 1g Light emitting device, 2 Light receiving device, 3 Indicator material, 4 Pump, 5 Piping, 6 Measurement cell, 7 Temperature controller, 8 Positioning jig, 9 Control unit, 10 Volatilization Organic matter sensor

Claims (13)

An indicator substance that changes from a first state to a second state by contact with a predetermined volatile organic substance;
A temperature control unit for controlling the temperature of the indicator substance;
A first light emitting device for irradiating the indicator substance with light of a first wavelength;
A second light emitting device for irradiating the indicator substance with light having a second wavelength different from the first wavelength;
A light receiving device that receives reflected light or transmitted light from the indicator substance and outputs an electrical signal; and
Irradiating the indicator substance with light of the first wavelength from the first light emitting device, observing a first electric signal output by receiving reflected or transmitted light from the indicator substance with the light receiving device, and Irradiating the indicator substance with light of the second wavelength from a second light emitting device, observing a second electrical signal output by receiving reflected or transmitted light from the indicator substance with the light receiving device, Based on one electric signal and the second electric signal, it is determined whether the indicator substance is in the first state or the second state, and the presence or absence of the volatile organic substance in the gas to be evaluated is evaluated. A volatile organic substance sensor comprising a control unit.   2. The volatile organic sensor according to claim 1, wherein the light receiving device functions as a light emitting diode that emits light having a wavelength longer than the first wavelength and the second wavelength by applying a voltage.   The indicator substance has a spectrum of reflected or transmitted light from the indicator substance in the second state compared to a spectrum of reflected or transmitted light from the indicator substance in the first state. 3. The volatile organic sensor according to claim 1, wherein the volatile organic substance sensor has different light intensities at one wavelength or at least one of the second wavelengths.   A third light emitting device for irradiating the indicator substance with light having a third wavelength different from both the first wavelength and the second wavelength, wherein the third wavelength is in both the first state and the second state. The light emitting device further comprises a third light emitting device that receives reflected light or transmitted light from the indicator substance and outputs a third electrical signal that is substantially the same from the light receiving device. 4. The volatile organic sensor according to any one of items 1 to 3.   5. The volatile organic substance sensor according to claim 1, wherein at least one of the first light emitting device and the second light emitting device is a light emitting diode.   6. The volatile organic substance sensor according to claim 1, wherein at least one of the first light-emitting device and the second light-emitting device is an electroluminescence element.   The first light emitting device, the second light emitting device, and the light receiving device reflect light from the first and second light emitting devices with the indicator material, and receive reflected light from the indicator material with the light receiving device. The volatile organic substance sensor according to any one of claims 1 to 6, wherein the volatile organic substance sensor is arranged so as to perform.   In the first light emitting device, the second light emitting device, and the light receiving device, light from the first and second light emitting devices transmits the indicator substance, and light transmitted from the indicator substance is received by the light receiving device. The volatile organic substance sensor according to any one of claims 1 to 6, wherein the volatile organic substance sensor is arranged so as to perform.   A positioning jig that includes a plurality of different indicator substances, and that changes a target substance of the plurality of light-emitting devices and the light-receiving device, and further, based on respective measurement results using the plurality of different indicator substances The volatile organic sensor according to any one of claims 1 to 8, wherein the gas to be evaluated is evaluated.   The volatile organic substance sensor according to any one of claims 1 to 9, further comprising a container that houses the indicator substance and makes the gas to be evaluated contact the indicator substance.   11. The volatile organic sensor according to claim 1, wherein the indicator substance is at least one selected from the group consisting of Nile red, metal porphyrin, and methyl red. The volatile organic substance sensor according to any one of claims 1 to 10, wherein the volatile organic substance sensor includes a first indicator substance.
A volatile organic substance sensor according to any one of claims 1 to 10 comprising a second indicator substance.
A volatile organic substance sensor characterized by calibrating the measurement result of the first indicator substance using the measurement result of the second indicator substance and evaluating the gas to be evaluated. A plurality of the volatile organic matter sensors according to any one of claims 1 to 8, or 10 comprising an indicator substance, each of the indicator substances being different from each other, based on the measurement results of the respective organic matter sensors, A volatile organic sensor characterized by evaluating a gas to be evaluated.

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