JP2007147585A - Apparatus for measuring liquid refractive index - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for measuring a liquid refractive index of high safety, high reliability and high precision, applied in a wide industrial field, and capable of compactifying a size. <P>SOLUTION: The apparatus includes a light source part 10, a sensor part 20 and a display part 30. Light gets incident from a light emitting diode 11 into a signal transmitting optical fiber 12, by making the an optical fiber 12 with a cleaved end face directly contact or neighbor closely to the light emitting diode 11. A refractive index measuring sensor 21 is manufactured by forming a metal thin layer, on a surface of the optical fiber with a core (optical fiber core) exposed by a chemical, by a vacuum evaporation method. A surface plasmon resonance phenomenon is generated when a liquid sample contacts with the refractive index measuring sensor 21. That is, the intensity of light output from the refractive index measuring sensor 21 varies in response to a refractive index of the liquid sample. A glass rod may be used in stead of the optical fiber core. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid refractive index measuring apparatus suitable for measuring a refractive index of alcohol or the like.

  Japanese Patent Laid-Open No. 2001-083084 (Patent Document 1) discloses a method for measuring the refractive index of a solution using an optical fiber. According to this publication, “If the incident light has an angular width, only light within a certain incident angle according to the refractive index of the liquid surrounding the fiber is transmitted by the principle of light transmission, and light with an incident angle higher than that is transmitted. Is based on the principle of leaking from the fiber. "

  Japanese Patent Application Laid-Open No. 2004-191110 (Patent Document 2) discloses a sensor for measuring a refractive index using an optical fiber core deposited with gold. In this publication, “a laser and a lens as a light source part, a sensor having a gold vapor deposition optical fiber and a sample introduction tube fixed to a glass tube as a sensor part, a detector and a multimeter as a detection part, a recorder and a computer as a recording part” There is a description of ".

  Academic Paper Analytical Chemistry, Vol. 52, No. 6, pages 433-438, 2003 (Non-Patent Document 1) used an optical fiber in which the exposed core was rotated by 90 degrees and gold deposition was repeated four times. Measuring the refractive index of alcohol with a sensor is disclosed.

  Academic paper Analytical Sciences, Vol. 18, No. 3, pp. 261-265, 2002 (Non-Patent Document 2) is based on a surface plasmon resonance sensor in which a coating film layer is formed on a gold thin film layer vacuum-deposited on a prism. Sensitive detection of amines is disclosed.

  In the scientific paper Analytical Sciences, Vol. 20, No. 4, pages 689-694, 2004 (Non-patent Document 3), a laser and a single spherical lens were used as a light source part, and gold was deposited once on the core as a sensor. A refractive index measuring device having higher sensitivity than a commercially available Abbe refractometer by using an optical fiber is shown.

JP 2001-083084 A (page 2) JP 2004-191110 A (page 4) Masatoshi Mitsuo and two others, "Quantitative analysis of alcohol using gold-deposited optical fiber refractive index sensor system", Analytical Chemistry, Japan, Japan Analytical Chemical Society, June 2003, Vol. 52, No. 6, 433-438 page Atsushi Nishimura, Toshifumi Yoshidome, and three others, “Application of a Surface Plasmon Resonance Sensor to Analyses of Amine Compounds with the Use of a Polymer Film and an Acid-base Reaction”, Analytical Sciences, Japan, Japan Analytical Chemical Society, 2002 March, Vol. 18, No. 3, pages 261-265 Masatoshi Mitsuo, Morihide Higo, “Simplification and Evaluation of a Gold-deposited SPR Optical Fiber Sensor”, Analytical Sciences, Japan, Japan Analytical Chemical Society, April 2004, Vol. 20, No. 4, 689-694 page

  However, Patent Document 1 has a problem that a complicated optical system is required by using a plurality of lenses, and parallel light needs to be incident with an angular width, and it is difficult to adjust the optical system. As a result, there are problems in accuracy and reproducibility due to aberrations and the like.

  Patent Document 2 discloses a light source unit composed of a laser and a single spherical lens, a sensor unit mainly composed of a refractive index measuring sensor, a glass tube for fixing the sensor, and a tube for inflowing / extracting a sample, and a sample container Therefore, there is a restriction for downsizing. In addition, the laser beam has a large burden on the eyes, and needs to be handled with care. Furthermore, since the laser consumes a large amount of power when emitting light, it is inconvenient for constructing a system that operates with low power such as a battery.

  Non-Patent Document 1 requires high technology to deposit gold four times on an optical fiber, and further improvement in measurement accuracy is desired.

  Non-Patent Document 2 requires a prism and a device for adjusting the angle and does not use an optical fiber. Therefore, further improvement is necessary for remote analysis, and the place where the device can be used is limited.

  Non-Patent Document 3 has succeeded in improving the performance of the refractive index measuring apparatus shown in Non-Patent Document 1 by using a laser as a light source and depositing gold once on an optical fiber, but using a laser as the light source Therefore, handling is difficult, and further downsizing is desired.

  An object of the present invention is to provide a refractive index measuring apparatus that can be applied to a wide range of industrial fields, can be easily downsized, and has high safety, reliability, and accuracy.

  As a result of earnest research, the inventor of the present application has found that a surface plasmon resonance effect can be obtained even with a light-emitting diode, and has solved the above problem by devising a method of injecting light into an optical fiber. That is, by using a light emitting diode as a light source, it has succeeded in eliminating the influence on the human body and at the same time reducing the power consumption. Furthermore, even if a glass rod is used as a medium for forming a metal thin film layer, it is found that the same result as that of an optical fiber can be obtained, and a sensor that can be applied to a wide range of industrial fields by properly using an optical fiber and a glass rod depending on the application. Department developed. In addition, the optical fiber is directly in close proximity to or close to the light source, eliminating the need for lens and optical axis alignment, and processing the optical signal that has passed through the sensor to digital display on the display unit, thereby reducing the size of the device. Successful. Further, by forming the light source unit and the display unit on one circuit, it is possible to provide a liquid refractive index measuring device that is smaller and easy to handle.

  The liquid refractive index measuring device according to the present invention is a light emitting diode and a detection for generating a surface plasmon resonance phenomenon corresponding to the refractive index of a liquid sample in contact with the surface of the light emitted from the light emitting diode. And a calculating means for obtaining a refractive index of the liquid sample based on the light output from the detecting means.

  According to the present invention, since the light emitting diode is used as the light source, the size can be reduced and the power consumption can be suppressed. In addition, since the output of the light emitting diode is stable, high reliability and accuracy can be obtained. In addition, high safety can be obtained as compared with a laser.

  Hereinafter, a liquid refractive index measurement device and a method of using the same according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of a liquid refractive index measurement apparatus according to an embodiment of the present invention. The liquid refractive index measurement device according to the present embodiment includes a light source unit 10, a sensor unit 20, and a display unit 30. However, the present invention is not limited to this. Here, the refractive index of the liquid is measured, whereby the mixing ratio and concentration of the liquid and the alcohol content of the liquor can be obtained.

  The light source unit 10 is provided with a light emitting diode 11, a signal transmission optical fiber 12, and an optical fiber connection instrument 13. Incidence of light from the light emitting diode 11 to the signal transmitting optical fiber 12 can be realized by bringing the optical fiber 12 whose end face is cleaved into close contact or close to the light emitting diode 11.

  The sensor unit 20 is provided with a refractive index measurement sensor 21, a reinforcing material 22, and a signal transmission optical fiber 23. The refractive index measuring sensor 21 is produced, for example, by forming a metal thin film layer by vacuum deposition on the surface of an optical fiber from which a core (optical fiber core) is exposed with a chemical. Although the length of the refractive index measurement sensor is about 3 to 100 mm, for example, by degreasing the optical fiber core with acetone and installing it at an appropriate distance from the vapor deposition source with a fixture, it is possible to make a short refractive index measurement sensor. A gold thin film can be formed as a metal thin film layer without unevenness. The refractive index measuring sensor 21 produced in this way is fixed to the reinforcing material 22. A glass rod may be used instead of the optical fiber core. When a liquid sample comes into contact with such a refractive index measurement sensor 21, a surface plasmon resonance phenomenon occurs. That is, the intensity of light output from the refractive index measurement sensor 21 (light that passes through the refractive index measurement sensor 21) changes according to the refractive index of the liquid sample. Since the response is obtained when the refractive index measuring sensor 21 comes into contact with the liquid sample, the reinforcing material 22 does not need to be tubular, and the reinforcing material 22 itself may not be provided. The signal transmission optical fiber 23 is connected to the light source unit 10 and the display unit 30 via an optical fiber connection device 13 and an optical fiber connection device 31 described later.

  The display unit 30 is provided with an optical fiber connection instrument 31, a signal transmission optical fiber 32, a light receiving element 33, a resistance element 34, an amplification unit 35, an A / D converter 36, a calculation unit 37, a display 38, and a ground 39. . When light enters the light receiving element 33 via the connection tool 31 and the optical fiber 32, a current is generated according to the intensity. This current is converted into a voltage by the resistance element 34, amplified by the amplifier 35, and input to the A / D converter 36. The signal converted into the digital signal by the A / D converter 36 is input to the calculation unit 37, and the calculation unit 37 calculates the refractive index and alcohol content of the liquid sample using the input digital signal, and the result is displayed on the display 38. Is displayed. The operation of the calculation unit 37 can be controlled by a program, and it is also possible to control a device (not shown) by monitoring a refractive index using a warning sound and / or opening / closing a valve.

  In such a liquid refractive index measurement device, light emitted from the light emitting diode 11 of the light source unit 10 enters the sensor unit 20. In the sensor unit 20, the surface plasmon resonance phenomenon occurs in the refractive index measurement sensor 21, and thus the transmitted light from the sensor unit 20 changes. Then, the change in the transmitted light is detected by the light receiving element 33, and the detected change in the transmitted light is output to the display 38 through the amplification unit 35, the A / D converter 36 and the calculation unit 37.

  According to such a liquid refractive index measuring apparatus, a wide range of refractive indexes can be measured with a simple optical system. In particular, the light-emitting diode 11 is sufficient, and a laser is unnecessary. Therefore, the light-emitting diode 11 is suitable for downsizing and easy to handle. Furthermore, by using an optical fiber, it is possible to measure a continuous refractive index in a remote place without relaying or amplifying. That is, by using such a liquid refractive index measuring device, it is also possible to construct an analysis and / or quality remote control system by refractive index measurement in a liquid production line. For example, a refractive index monitoring mechanism that warns with a sound such as a buzzer when the signal from the sensor unit 20 satisfies a preset condition and / or a device control mechanism such as opening and closing of a valve may be configured. .

  When an optical fiber core is used for the refractive index measurement sensor 21, the optical fiber core is, for example, a commercially available optical fiber configured by coating a high refractive index light transmission medium with a low refractive index polymer or the like. It is possible to use those obtained by removing the portion (such as a polymer having a low refractive index).

  As the refractive index measuring sensor 21, for example, a single film of gold, silver, copper or aluminum, or a metal film having a multilayer structure of a film of silver, copper and / or aluminum and a gold film is used for an optical fiber core or a glass rod. What was vapor-deposited on the surface can be used. The total thickness of the metal films is preferably 10 nm to 70 nm. Moreover, it is preferable to cleave the end face.

  By selecting the material of the light transmission member constituting the refractive index measuring sensor 21 from a quartz glass rod having excellent mechanical strength and an optical fiber core capable of constructing a small sensor, it can be applied to a wide range of industrial fields. A sensor for refractive index measurement can be provided.

  Moreover, as the light emitting diode 11, what emits monochromatic light or white light can be used.

  A photodiode or the like can be used as the light receiving element 33.

  Further, no lens is required between the light source unit 10 and the sensor unit 20.

  The display unit 30 may display not only the refractive index of the liquid sample itself but also the alcohol content obtained from the refractive index.

  Further, if the light emitting diode 11 or the light receiving element 33 can be brought into close contact or close to the refractive index measuring sensor 21, the signal transmitting optical fibers 12 and 32 and the optical fiber connecting devices 13, 23 and 31 are used. May not be provided. That is, the light may be directly incident on the refractive index measurement sensor 21 from the light emitting diode 11 or the output from the refractive index measurement sensor 21 may be directly measured.

  As the liquid sample, it is preferable to use water and / or an organic substance as a solvent, and it is more preferable not to corrode the sensor.

  FIG. 2 shows the response characteristics with respect to the refractive index when the light-emitting diode 11 having a diameter of 5 mm having a different color or light emission shape is used. As the refractive index measuring sensor 21, a 10 nm long optical fiber core having a 45 nm gold film deposited on the surface thereof was used. The red light emitting diode in FIG. 2 has a wide directional type and a middle directional type. In the wide directional type, light spreads radially from the light emitting point, and in the middle directional type, light is condensed in a specific direction. Both are commercially available. The refractive index was adjusted by changing the concentration of the ethylene glycol methanol solution. This experiment shows that the sensor characteristics such as response range and sensitivity can be controlled simply by changing the color of the light emitting diode.

(Comparative Example 1)
Refraction when a He—Ne laser is used instead of the light source unit 10 and the intensity of light transmitted through the sensor is measured using a Si detector and analyzed by a computer via an optical multimeter and a digital multimeter. The response characteristics with respect to the rate are shown in FIG. As a refractive index measuring sensor, a 10-cm long optical fiber core having a 45 nm gold film deposited thereon was used, and measurement was performed using methanol solutions of various alcohols. Although it has a response characteristic similar to that of the first embodiment, the device is very large and unsuitable for carrying.

  FIG. 4 shows the intensity change of light transmitted through the sensor when the light source is a light emitting diode 11 having a diameter of 3 mm and the refractive index is changed. As the refractive index measurement sensor 21, a 10-cm long optical fiber core having a 45 nm gold film deposited thereon was used, and an ethylene glycol methanol solution was used as a measurement sample. A sufficient response was obtained even with the light emitting diode 11 having a small diameter. Also, a sensor system could be constructed for the white light emitting diode 11.

  FIG. 5 shows a response characteristic (calibration curve) for a slight change in refractive index in the range of 1.330 to 1.353 when the red light emitting diode 11 (wide directional type) having a diameter of 5 mm according to the present invention is used. As a sensor for refractive index measurement, a metal film having a 45 nm gold film deposited on the surface of an optical fiber core having a length of 10 cm was used. As a measurement sample, a methanol solution of benzyl alcohol was used. The correlation coefficient is on a straight line of 0.996, indicating that small changes in refractive index can be measured quantitatively.

  In FIG. 6, the result of the ethanol concentration measurement of distilled liquor using this invention is shown. A red light emitting diode having a diameter of 5 mm was used as the light source. In this example, a calibration curve of 0 to 50 degrees at 15 ° C. was prepared in advance using the refractive index measurement sensor 21 in which a 45 nm gold film was deposited on the surface of an optical fiber core having a length of 10 cm. The sample was measured to calculate the concentration. In the present invention, it is also possible to measure the frequency instantaneously by registering a calibration curve in the calculation unit in advance. Since the surface plasmon resonance phenomenon is used, the ethanol concentration can be obtained regardless of whether the sample is colored. In this example, we have succeeded in accurately determining the concentration of 2 brands of shochu (Shiranami (trademark), Isanishiki (trademark)), whiskey, brandy, gin, vodka, lamb and tequila, and also applied to industry. It was shown to be possible.

  FIG. 7 shows a calibration curve of an aqueous ethanol solution at 15 ° C. measured using a red light emitting diode 11 (wide directional type) having a diameter of 5 mm and a relative standard deviation in three measurements. As the refractive index measuring sensor 21, a 10 nm long optical fiber core having a 45 nm gold film deposited on the surface thereof was used. The response curve decreases monotonically with increasing ethanol concentration. The relative standard deviation at each point was 0.07% at the maximum, and the concentration could be measured with high accuracy.

(Comparative Example 2)
FIG. 8 shows a calibration curve of an aqueous ethanol solution at 25 ° C. and a relative standard deviation in three measurements when a He—Ne laser is used as a light source and an intensity change of light transmitted through an optical fiber is observed. As a sensor for refractive index measurement, a metal film having a 45 nm gold film deposited on the surface of an optical fiber core having a length of 10 cm was used. Although a monotonically decreasing response curve according to the concentration was obtained, the relative standard deviation of each point was 1.8% at the maximum, which is somewhat dissatisfied with respect to accuracy.

  In FIG. 9, a refractive index measuring sensor 21 having a diameter of 1 mm, 2 mm, 2.5 mm, and 5 mm on which a gold film is formed is used, and the refractive index measuring sensor 21 is a light emitting diode. 11 shows a response characteristic with respect to the refractive index of the sensor system in direct contact with the photosensor 11 and the light receiving element 33. The refractive index was adjusted using an aqueous ethanol solution or a methanol solution of ethylene glycol. In addition, the thing of 2 mm is an extract of the result measured over the wide refractive index range. As shown in FIG. 9, the intensity of transmitted light decreased with increasing refractive index in glass rods of all diameters, and a good response was obtained also in the glass rod. Moreover, high sensitivity was obtained in a glass rod of 2 mm or less. From these results, it was confirmed that a sufficient response could be obtained even with a glass rod, and it was shown that the optimum strength and sensitivity could be selected by selecting the diameter of the glass rod.

  FIG. 10 shows the response characteristics with respect to the refractive index when the light emitting diode 11 having a diameter of 5 mm and having a different color is used in the present invention. As the refractive index measuring sensor 21, a quartz glass rod having a diameter of 2 mm and a 45 nm gold film formed on the surface thereof was used. The refractive index was adjusted by changing the concentration of the ethylene glycol methanol solution. By changing the color of the light-emitting diode, the response characteristics could be changed with high sensitivity as in the case of the optical fiber.

  In the present invention, as a refractive index measuring sensor 21, a response characteristic with respect to the refractive index of a sensor in which a quartz glass rod having a diameter of 2 mm is heated and deformed into a U shape and a 45 nm gold film is formed on the lower surface thereof is shown in FIG. Show. A red light emitting diode 11 having a diameter of 5 mm was used as a light source. The refractive index was adjusted by changing the concentration of the ethylene glycol methanol solution. From these results, it was found that a good response was obtained when the radius of curvature was increased, and that a deformed glass rod could be used as a sensor with an appropriate curvature.

(Comparative Example 3)
FIG. 12 shows the response characteristics with respect to the refractive index of a glass rod having a radius of curvature of 21 mm and not deposited with gold. The refractive index was adjusted by changing the concentration of the ethylene glycol methanol solution. It was shown that the surface plasmon resonance effect did not occur in the glass rod when no gold thin film was deposited, and no response was shown.

It is a figure which shows the basic composition of the liquid refractive index measuring apparatus which concerns on embodiment of this invention. 4 is a graph showing differences in response characteristics depending on colors of light emitting diodes 11. It is a graph which shows the response characteristic with respect to the refractive index at the time of using He detector for a light source and Si detector, an optical multimeter, and a digital multimeter for the detection of light intensity. It is a graph which shows the response characteristic with respect to refractive index at the time of using a light emitting diode for a light source, and Si detector, an optical multimeter, and a digital multimeter for the detection of light intensity. Refractive index: It is a graph which shows the response characteristic (calibration curve) in the range of 1.330-1.353. It is a figure which shows the measurement result of the ethanol concentration in distilled liquor using the apparatus which concerns on embodiment of this invention. It is a graph which shows the calibration curve and relative standard deviation of the ethanol aqueous solution obtained when the apparatus which concerns on embodiment of this invention is used. It is a graph which shows the analytical curve and relative standard deviation of ethanol aqueous solution at the time of using a Si detector, an optical multimeter, and a digital multimeter for the detection of light intensity for a He-Ne laser as a light source. It is a graph which shows the response characteristic of ethanol aqueous solution at the time of using what formed the metal film on the surface of the quartz glass rod as the sensor 21 for refractive index measurement. FIG. 5 is a graph showing response characteristics with respect to refractive indexes of light emitting diodes of various colors, using a refractive index measuring sensor 21 having a quartz glass rod formed with a metal film on the surface. It is a graph which shows the response characteristic with respect to refractive index at the time of using what formed the metal film on the surface of the quartz glass rod deform | transformed into the U shape as the sensor 21 for refractive index measurement. It is a graph which shows the response characteristic with respect to refractive index at the time of using the quartz glass rod which deform | transformed into the U shape as the sensor 21 for refractive index measurement, and does not vapor-deposit gold | metal | money.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light source part 20 Sensor part 30 Display part 11 Light emitting diode 12 Optical fiber for signal transmission 13 Optical fiber connection tool 21 Refractive index measurement sensor 22 Refractive index measurement sensor reinforcement 23 Signal transmission optical fiber 31 Optical fiber connection tool 32 Signal transmission Optical fiber 33 Light receiving element 34 Resistive element 35 Amplifying part 36 A / D converter 37 Arithmetic part 38 Display 39 Ground

Claims (5)

A light emitting diode;
Detection means for generating a surface plasmon resonance phenomenon corresponding to the refractive index of the liquid sample in contact with the surface of the light emitted by the light emitting diode;
A calculation means for obtaining a refractive index of the liquid sample based on the light output from the detection means;
A liquid refractive index measuring apparatus comprising: The detection means includes
A light transmission member;
A metal film formed on the surface of the light transmission member;
The liquid refractive index measuring device according to claim 1, wherein   The liquid refractive index measurement apparatus according to claim 2, wherein the light transmission member is an optical fiber core or a glass rod.   The liquid refractive index measuring apparatus according to claim 1, further comprising display means for displaying the refractive index.   5. The liquid refraction according to claim 1, wherein the detection unit is disposed at a position remote from at least one selected from the group consisting of the light emitting diode and the calculation unit. Rate measuring device.

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