JP4918678B2 - Acetic acid concentration sensor - Google Patents

Description

  The present invention relates to an acetic acid concentration detection sensor, and particularly measures a change in transmitted light intensity of an optical fiber and detects the concentration of acetic acid based on the change.

  Recently, many organic acids are overflowing around us. Especially, acetic acid is widely used in sour foods, and it is important in the food field because it is generated by the deterioration of alcohol and various foods. For this reason, if the acetic acid concentration can be measured easily and quickly, it can be applied not only to the food field but also to the medical field and others. Therefore, development of a simple acetic acid concentration detection sensor is strongly desired.

  As a conventional acetic acid measurement sensor, for example, a sensor using bacteria that selectively assimilate acetic acid is known (see Patent Document 1). However, although this acetic acid measurement sensor is superior in response to acetic acid as compared with a plurality of organic acids other than acetic acid, it cannot detect depending on the acetic acid concentration.

On the other hand, the present inventors have already proposed a humidity sensor using a change in transmitted light intensity of an optical fiber (see Patent Document 2). This humidity sensor has a moisture-sensitive clad layer formed around the core of a plastic optical fiber. Utilizing the fact that the refractive index of the cladding layer changes with humidity, the transmitted light intensity of the light passing through the optical fiber is measured, and the structure is simple and easy to handle.
Japanese Patent Laid-Open No. 10-201469 JP 2003-130863 A

The inventors of the present invention have made extensive studies on the clad material that swells in accordance with the acetic acid concentration using the measurement principle of the humidity sensor based on the change in transmitted light intensity of the optical fiber. As a result, the inventors have invented an acetic acid concentration detection sensor.
Therefore, the problem to be solved by the present invention is to provide an acetic acid concentration detection sensor capable of accurately and quickly detecting the acetic acid concentration by a simple means.

Acetate concentration detection sensor of the present invention, Ru comprises a sensor head sensitive cladding layer is formed of the refractive index changes depending on the swell and acetic acid concentrations in the presence of acetic acid around the core of the optical fiber. Then, the above-sensitive cladding layer, wherein the copolymer der Rukoto the copolymer or lauryl methacrylate and ethylene glycol dimethacrylate and menthyl methacrylate and benzyl methacrylate.

  In consideration of the fact that acetic acid is both an amphiphilic substance and a polar substance, selection of a copolymer having a high fat solubility as described above is effective.

  According to the present invention, since the degree of swelling of the sensitive cladding layer varies depending on the acetic acid concentration, and the refractive index of the sensitive cladding layer varies accordingly, the transmitted light intensity of light passing through the optical fiber depends on the acetic acid concentration. Will be different. Therefore, the acetic acid concentration can be detected by measuring the transmitted light intensity. This acetic acid concentration detection sensor can be used not only in the above-described food field but also in the medical field for the purpose of monitoring the defecation of bedridden elderly people, for example, since acetic acid is contained in the stool.

  Hereinafter, the best mode for carrying out an acetic acid concentration detection sensor according to the present invention will be described in detail with reference to the accompanying drawings. 1 to 5 show an embodiment of an acetic acid concentration detection sensor according to the present invention. As shown in FIG. 1, this acetic acid concentration detection sensor has a configuration in which a sensor head 2 is provided on a part of an optical fiber 1. The commercially available optical fiber 1 is composed of a core 3 at the center, a clad 4 covering the periphery thereof, and a skin 5 covering the clad 4, and a part of the clad 4 of the optical fiber 1 is formed. The sensor head 2 is configured by forming a sensitive clad that swells in the presence of acetic acid, that is, a sensitive clad layer 6 on the exposed surface of the core 3 after being removed. In the commercially available plastic optical fiber 1, the core 3 is generally made of polymethylmethacrylic acid (PMMA) and the clad is made of a low refractive index polymer. And benzylmethacrylic acid copolymer (P- (MtMA-co-BzMA)) or laurylmethacrylic acid and ethylene glycol dimethacrylic acid copolymer (P- (LaMA-co-EGMA)) Yes. These copolymer polymers have the property of swelling by adsorbing acetic acid molecules and lowering the refractive index. In addition to the above two types of copolymer polymers, the present inventors have demonstrated through experiments that a copolymer polymer containing methacrylic acid acts on the object of the present invention. The copolymer (P- (MtMA-co-BzMA) has a structural formula as shown in FIG. 2 and is known to have characteristics as a photofunctional polymer (Japan Application). (See Journal of Physics Society Vol.37 (1998) pp.4405-4408).

  The sensitive cladding layer 6 can be formed by dip-coating the copolymer 3 on the surface of the core 3 of the optical fiber 1. However, when dip-coating, the refractive index is low for the purpose of controlling the refractive index of the sensitive cladding layer 6. A rate polymer or a surfactant may be added. In this case, for example, polyvinylidene fluoride is effective as the low refractive index polymer, and a fluorinated surfactant such as FC4430 (manufactured by Sumitomo 3M) is effective as the surfactant.

  Table 1 shows the difference in refractive index between the core 3 made of PMMA and the sensitive cladding layer 6 made of the copolymer. As is apparent from Table 1, the initial refractive index of the sensitive cladding layer 6 is larger than that of the core 3.

  FIG. 3 shows how the refractive index of P- (MtMA-co-BzMA) + FC4430 varies depending on the measurement time in an acetic acid solution having a concentration of 10%. The refractive index was measured with an Abbe measuring rate meter. The refractive index of P- (MtMA-co-BzMA) + FC4430, which had an initial refractive index of 1.516, decreased to a refractive index of 1.488 after 15 minutes and further decreased to a refractive index of 1.486 after 20 minutes. Moreover, since the refractive index of PMMA maintains 1.49 and does not change, it is considered that the refractive index of P- (MtMA-co-BzMA) + FC4430 is reversed from PMMA 5 to 6 minutes after the start of measurement.

  FIG. 4 shows the principle when the acetic acid concentration is detected by the acetic acid concentration detecting sensor having the above configuration. Since the refractive index of the sensitive cladding layer 6 of the sensor head 2 changes depending on the acetic acid concentration, the transmitted light intensity when the incident light 7 incident from one end of the optical fiber 1 passes through the sensor head 2 is expressed as the other end of the optical fiber 1. The acetic acid concentration is detected by measuring as the outgoing light 8 emitted from. FIG. 4A shows the intensity of transmitted light when the acetic acid concentration detection sensor is arranged in a solution other than acetic acid or in an acetic acid solution having a very low acetic acid concentration. In this case, since the sensitive cladding layer 6 does not swell, the refractive index of the sensitive cladding layer 6 is larger than that of the core 3, and the core 3 does not function as a waveguide. For this reason, most of the incident light 7 incident on the optical fiber 1 leaks from the core 3 into the sensitive cladding layer 6 in the sensor head 2, and the outgoing light 8 emitted from the other end of the optical fiber 1 is very small. It will be a thing.

  On the other hand, FIG. 4B shows the magnitude of transmitted light intensity when the acetic acid concentration detection sensor is arranged in an acetic acid solution or acetic acid gas. When the acetic acid concentration is high to some extent, the sensitive cladding layer 6 gradually swells with time due to the incorporation of acetic acid according to the acetic acid concentration, and the refractive index gradually decreases as the density of the sensitive cladding layer 6 decreases. Thus, in the sensor head 2, when the refractive index of the sensitive cladding layer 6 is smaller than that of the core 3, the core 3 functions as a waveguide. As a result, most of the incident light 7 incident from one end of the optical fiber 1 is reflected by the sensitive cladding layer 6 in the sensor head 2, so that the transmitted light intensity increases, and the emitted light 9 from the other end of the optical fiber increases. It will be. Thus, since the degree of swelling in the sensitive cladding layer 6 in the sensor head 2 has a correlation with the acetic acid concentration, the acetic acid concentration can be monitored by measuring the transmitted light intensity of the light that has passed through the acetic acid concentration detecting sensor. Become.

FIG. 5 shows a method for producing an acetic acid concentration detection sensor according to the present invention. FIG. 5A shows a commercially available plastic optical fiber 1. The optical fiber 1 is composed of a core 3 near the center, a clad 4 covering the periphery thereof, and a skin 5 covering the clad 4, and such a commercially available optical fiber 1 is prepared with an appropriate length.

  First, as shown in FIG. 5 (b), the outer skin 5 of the optical fiber 1 is cut by a cutter over the entire circumference by an appropriate length l. The length l determines the total length of the sensor head, and is not particularly limited, but is preferably about 3 to 5 cm in consideration of sensitivity as a sensor.

  Next, the optical fiber 1 is immersed in 1,4-dioxane in order to remove the clad 4 in the part where the skin 5 is cut off. The clad is etched in about 10 minutes, and as shown in FIG. 5C, the surface 3a of the core 3 appears in the portion where the clad 4 is removed. Most of the commercially available plastic optical fibers 1 have a core 3 having a diameter of about 1 mm. However, as shown in FIG. 5D, in this embodiment, a ratio of 3: 1 of 1,4-dioxane and chloroform is further added. The sensitivity of the sensor is increased by immersing and etching the core 3 in the solution mixed in step 1 to further reduce the diameter d of the core 3. In this case, it is preferable to reduce the diameter d of the core 3 to about 0.25 to 1 mm.

  The copolymer P- (MtMA-co-BzMA) is obtained by randomly copolymerizing menthyl methacrylic acid and benzyl methacrylic acid having a monomer ratio of 1: 1 under the reaction initiator benzoyl peroxide. Therefore, this P- (MtMA-co-BzMA) is dissolved in chloroform at a concentration of 1 to 7% to obtain a clad solution. The optical fiber 1 after the skin 5 and the clad 4 are removed is immersed in the clad liquid, and P- (MtMA-co-BzMA is applied to the exposed surface 3a of the core 3 as shown in FIG. ), And pulled up from the cladding solution, and then dried at room temperature for about 24 hours to form the sensitive cladding layer 6. At that time, as described above, the refractive index of the sensitive cladding layer 6 can be controlled by mixing FC4430, PVDF, or the like into the cladding liquid. The thickness of the sensitive cladding layer 6 affects the sensitivity to acetic acid and the swelling speed. In the present invention, the thickness of the sensitive cladding layer 6 is applied in the range of 0.5 to 10 μm, and preferably in the range of 1 to 7 μm. The thickness of the sensitive cladding layer 6 can be adjusted by the immersion time. In this way, an acetic acid concentration detection sensor provided with the sensor head 2 is completed. Even when P- (LaMA-co-EGMA) is formed as a sensitive cladding layer, lauryl methacrylic acid and ethylene glycol dimethacrylic acid having a monomer ratio of 1: 1 are added under the reaction initiator benzoyl peroxide as described above. Is randomly copolymerized to obtain P- (LaMA-co-EGMA), which is dissolved in chloroform to obtain a clad solution.

  FIG. 6 shows an example of the configuration of an acetic acid concentration detection system incorporating the acetic acid concentration detection sensor having the above-described configuration. In this acetic acid concentration detection system, a part of the optical fiber 1 including the sensor head 2 of the acetic acid concentration detection sensor is set in the solution tank 10. The solution tank 10 is filled with an acetic acid solution 11 whose concentration is to be measured, and the sensor head 2 is immersed in the acetic acid solution 11. A semiconductor laser device 12 and a photodetector 13 incorporating a photodiode are connected to both ends of the optical fiber 1 protruding to both sides of the solution tank 10. Then, a laser beam of λ = 670 nm is incident from the one end 1 a of the optical fiber 1 from the semiconductor laser device 12, and the transmitted light intensity after passing through the sensor head 2 is detected as the output light amount from the other end 1 b of the optical fiber 1. Measure with the instrument 13. The electrical signal from the photodetector 13 is sent to the digital voltmeter 14 for digital conversion, and then displayed as an acetic acid concentration value on the display 15 of the computer.

  Next, the results of experiments on the responsiveness of the acetic acid concentration detection sensor according to the present invention to acetic acid using the above-described acetic acid concentration detection system will be described.

Example 1
The response of several kinds of copolymer to acetic acid was investigated. A sensor sample was prepared by forming a sensitive clad layer on the surface of a core (PMMA) having a diameter of 0.5 mm and a sensor head length of 4 cm, and the response to acetic acid having a concentration of 5 wt% was examined using the acetic acid concentration detection system. . There are four types of sensitive cladding layers formed on the surface of the core: P- (MtMA-co-BzMA) + FC4430, P- (LaMA-co-EGMA) + FC4430, PMMA + PVDF (3: 1), and PMMA. FIG. 7 shows the result. According to Fig. 7, P- (MtMA-co-BzMA) + FC4430 and P- (LaMA-co-EGMA) + FC4430 are superior in response compared to the other two types, and are used as cladding materials for acetic acid concentration detection sensors. I found that it was available.

Example 2
The response of the acetic acid concentration detection sensor to the acetic acid concentration was investigated. An acetic acid concentration detection sensor for a sample was manufactured by forming P- (MtMA-co-BzMA) as a sensitive cladding layer on the surface of a core (PMMA) having a diameter of 0.5 mm and a sensor head length of 4 cm. The chloroform solution concentration of P- (MtMA-co-BzMA) is 5 wt%. Using the acetic acid concentration detection system, the reactivity with respect to four types of acetic acid concentrations of 10 wt% concentration, 7 wt% concentration, 5 wt% concentration, and 3 wt% concentration was examined. As a comparative example, the response to water was also examined at the same time. FIG. 8 shows the result. According to this, as the acetic acid concentration increased, the transmitted light intensity when passing through the sensor head increased, and the responsiveness was good when the acetic acid concentration was 3 wt% or more. On the other hand, it was confirmed that sufficient response to water was not exhibited.

Example 3
The response of the acetic acid concentration detection sensor to various acids other than acetic acid was investigated. The same sensor sample as in Example 2 was used. Using the acetic acid concentration detection system, responsiveness to 10 wt% acetic acid, 10 wt% lactic acid, 10 wt% citric acid monohydrate, and 10 wt% hydrochloric acid was examined. FIG. 9 shows the result. According to this, it was confirmed that the response with acetic acid was superior to other organic acids other than acetic acid and hydrochloric acid. That is, the present invention is useful as a sensor for detecting the acetic acid concentration.

  The acetic acid concentration detection sensor according to the present invention can be easily used in the food field and the medical field because the means for detecting the acetic acid concentration is simple.

It is sectional drawing which shows the structure of the sensor head of the acetic acid concentration detection sensor which concerns on this invention. It is a structural formula of a copolymer of menthyl methacrylic acid and benzyl methacrylic acid. It is a graph which shows the change of the refractive index with respect to the measurement time of a copolymer. It is explanatory drawing which showed the detection principle by the acetic acid concentration detection sensor of this invention. It is process drawing which shows the preparation methods of an acetic acid concentration detection sensor. It is a block diagram of the acetic acid concentration detection system incorporating the acetic acid concentration detection sensor of this invention. It is a graph which shows the result of Example 1 investigated about the responsiveness of several types of copolymer to acetic acid. It is a graph which shows the result of Example 2 investigated about the responsiveness of the acetic acid concentration detection sensor with respect to an acetic acid concentration. It is a graph which shows the result of Example 3 investigated about the responsiveness of the acetic acid concentration detection sensor with respect to various acids other than acetic acid.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber 2 Sensor head 3 Core 4 Clad 5 Skin 6 Sensitive clad layer 10 Solution tank 11 Acetic acid solution 12 Semiconductor laser apparatus 13 Photo detector 14 Digital voltmeter 15 Display

Claims (5)

A sensor head in which a sensitive cladding layer that swells in the presence of acetic acid and whose refractive index changes according to the concentration of acetic acid is formed around the core of the optical fiber ;
An acetic acid concentration detection sensor, wherein the sensitive cladding layer is formed of a copolymer of menthyl methacrylic acid and benzyl methacrylic acid or a copolymer of lauryl methacrylic acid and ethylene glycol dimethacrylic acid . The sensitive cladding layer, acetate concentration detection sensor of claim 1, wherein polyvinylidene fluoride or fluorinated surfactants are those that have been mixed as a low refractive index polymer to the copolymer. The acetic acid concentration detection sensor according to claim 1, wherein the acetic acid concentration is measurable in a range of 3 to 10% by weight. The acetic acid concentration detection sensor according to claim 1, wherein the sensitive clad layer swells in the presence of liquid or gas. The acetic acid concentration detection sensor according to claim 1, wherein the acetic acid concentration is detected by measuring a transmitted light intensity when passing through the sensor head.

Images