JP6224410B2 - pH measuring method and apparatus - Google Patents

Description

  The present invention relates to a pH measurement method and apparatus, and more particularly to a method and apparatus for measuring a pH value from a color (hereinafter simply referred to as color development) indicated by a pH indicator.

  Conventionally, a method (colorimetric analysis method) for easily grasping a pH value using a pH test paper (such as a litmus test paper) in which a paper or the like is impregnated with a pH indicator has been widely used. However, the pH test paper must be visually judged by the worker, and the judgment of the pH value may be different for each worker, so there is a risk of lack of objectivity. For this reason, in the field of cell culture, the color development of the pH indicator added to the culture solution is directly measured by a colorimeter such as a spectrophotometer or a colorimeter so that anyone can objectively determine the pH value. A method of measuring or indirectly measuring through a color image or the like and measuring a pH value based on the measured value has been developed (see Patent Documents 1 to 3).

  FIG. 12A shows an example of a pH value measurement system disclosed in Patent Document 2. The system of the illustrated example obtains the pH value of the culture medium 43 from the color of the pH indicator (phenol red) added to the cell culture medium 43 enclosed between the main body 42 and the lid 44 of the dish 41. , A lighting control device 48 that illuminates the dish 41 from below the mounting table 47, an imaging device 49 that captures a color image of the dish 41 from above the mounting table 47, and the color image is red An imaging control device 51 is provided that sends an RGB signal composed of a component (R signal), a green component (G component), and a blue component (B signal) to the computer 52.

  The computer 52 in FIG. 12A calculates a ratio (B / G ratio) between the G signal and the B signal in the color image, and applies the B / G ratio to the functional expression in FIG. Calculate the pH value. The relational expression in FIG. 5B is that the B / G ratio is calculated from the color images of a plurality of samples of the phenol red-added culture medium 43 having different pH values, and the pH value and the B / G ratio of each sample are calculated by regression analysis. The relationship is statistically estimated as a quadratic function (linear regression model). When the pH value changes, the G signal and the B signal change more greatly than the R signal in the phenol red-added medium. Therefore, the pH value of the medium 43 is calculated from the B / G ratio in the color image according to the relational expression in FIG. Can be estimated uniquely. The B signal and G signal (blue and green intensity) in the color image vary depending on the depth of the culture medium 43, but the ratio of both signals (B / G ratio) does not change. Based on the G ratio, a pH value that does not depend on the depth of the medium 43 can be calculated.

Japanese Patent Laid-Open No. 2-109970 JP 2007-163350 A Special table 2012-215428 gazette JP 2012-163484 A

Kume Hitoshi et al. "Series Introduction Statistical Method 2 Regression Analysis" Iwanami Shoten Co., Ltd., published in October 1987, pp. 134-135

  However, the method of measuring the pH value from the B / G ratio in the color development (color image) of the pH indicator as shown in FIG. 12 can be applied to a pH indicator such as phenol red having a relatively narrow discoloration range. When applied to a pH indicator with a wide color change range, there is a problem that the measurement accuracy of the pH value may be lowered. That is, the phenol red with a color change range of pH = 6.5 to 8.5 can be modeled as a quadratic function (linear regression model) with the B / G ratio, but when the color change range of the pH indicator is widened Since the color development changes in a complicated manner, it becomes difficult to model the relationship between the pH value and the B / G ratio with a quadratic function or the like. Development of a technique capable of accurately estimating the pH value from the color of the pH indicator is desired regardless of the wide or narrow color change range of the pH indicator.

  It is also envisaged that pH indicators with different colors must be combined to widen the color change range. Even if the color development of the pH indicator is complicated or a combination of a plurality of pH indicators, the present inventor has specific color signals (for example, B signal and G signal) during the color development of the pH indicator as shown in FIG. In addition, the idea was that it was possible to correspond to the pH value by considering all the color signals (entire color development). In fields such as environmental monitoring, research and development of pH indicators that can accurately measure pH of water, air / atmosphere, geology, etc. over a long period of time is underway (see Patent Document 4). In order to meet the demand, development of a technique capable of estimating the pH value in consideration of the entire color development indicated by the pH indicator is required.

  Accordingly, an object of the present invention is to provide a pH measurement method and apparatus capable of estimating the pH value in consideration of the entire color development of the pH indicator.

  Referring to the embodiment of FIG. 1 and the flow chart of FIG. 3, in the pH measurement method according to the present invention, the white point O is the center of color development of each of the pH indicators Q brought into contact with the samples S1, S2,. Are plotted on a chromaticity diagram M (see FIG. 2) arranged at, and white points O are detected as declination angles D1, D2,... The relational expression F () between the pH values of the specimens S1, S2,... And the deviation angles D1, D2,... Of the coloring points C1, C2,. 5 to 8) is set, the deviation angle Dt of the color development point Ct is detected from the color development when the pH indicator Q is brought into contact with the measurement target T, and the color development point of the pH indicator Q brought into contact with the measurement subject T The pH value of the measurement target T is calculated from the deviation angle Dt of Ct and the relational expression F.

  Referring to the block diagram of FIG. 1, the pH measuring device according to the present invention receives a color signal of pH indicator Q, and the color development is a chromaticity diagram M in which a white point O is arranged at the center (see FIG. 2). ) Detection means 27 for detecting the deviation angle D of the coloring point C on the polar coordinates centered on the white point O plotted on the above, the pH values of the samples S1, S2,. The storage means 21 for storing the relational expression F (see FIGS. 5 to 8) with the deviation angles D1, D2,... Of the coloring points C1, C2,. The calculation means 29 is provided for calculating the pH value of the measurement target T from the deviation angle Dt of the coloring point Ct when Q is brought into contact with the measurement target T and the relational expression F. As shown in FIG. 1, the pH measuring device according to the present invention includes the pH values of the samples S1, S2,... Having different pH values and the color development point of the pH indicator Q brought into contact with the samples S1, S2,. Setting means 28 for setting the relational expression F by inputting the declination angles D1, D2,... Of C1, C2,.

  Preferably, as shown in FIG. 1, a film 11 containing a pH indicator Q and a colorimeter 12 facing the film 11 are provided, and the color signal of the pH indicator Q is used as an output signal of the colorimeter 12 as a pH signal. Calculate the value. Alternatively, in place of the colorimeter 12, a film 11 containing the pH indicator Q and a camera (not shown) for taking a color image of the film 11 are provided, and the pH value is determined using the color signal of the pH indicator Q as a color image. It is also possible to calculate.

More preferably, the chromaticity diagram M with the white point O arranged at the center is projected from the white point of the RBG color space as shown in FIG. 2 to the CIExy chromaticity diagram M1 as shown in FIG. A cross-sectional view M3 parallel to the a ^* b ^* plane of the L ^* a ^* b ^* color space as shown in FIG. M2 or FIG. Desirably, as shown in FIGS. 5 to 8, the relational expression F is expressed as the color of the pH indicator Q brought into contact with each sample S1, S2,... With the pH values of different samples S1, S2,. A logistic regression curve having the dependent angles D1, D2,... At points C1, C2,.

  The pH measuring method and apparatus according to the present invention plots the color development of the pH indicator Q on the chromaticity diagram M in which the white point O is arranged at the center, and the white point O is the declination of the color development point C on the polar coordinates of the center. D is detected, and the pH values of the samples S1, S2,... Having different pHs in advance and the declination angles D1, D2 of the coloring points C1, C2,. ,... Are set, and the pH value of the measurement target T is calculated from the deviation angle Dt of the coloring point Ct when the pH indicator Q is brought into contact with the measurement target T and the relational expression F. Therefore, it produces the following effects.

(A) The color development of the pH indicator Q is detected by plotting the color development of the pH indicator Q on the chromaticity diagram M, detecting the deviation angle D of the color development point C, and estimating the pH value from the deviation angle D. The pH value can be estimated in consideration.
(B) Even when the pH indicator Q having a wide color change range is used, the pH value can be accurately measured by considering the entire color change, and the color development of the pH indicator Q regardless of the range of the color change range of the pH indicator Q. It becomes possible to measure pH value from.
(C) By measuring the pH value in consideration of the entire color development of the pH indicator Q, it is possible to cope with a pH indicator in which the color development changes in a complicated manner. It is also possible to measure the pH value.

Hereinafter, embodiments and examples for carrying out the present invention will be described with reference to the accompanying drawings.
These are explanatory drawings of one Example of the pH measuring apparatus by this invention. These are explanatory drawings of an example of the chromaticity diagram M (and the deflection angle D of the coloring point C) used in the present invention. These are examples of a flow chart showing a pH measurement method according to the present invention. These are explanatory drawings of pH indicators Q1, Q2a, Q2b, Q3a, Q3b, and Q4 having different color change ranges. Is an example of a relational expression F1 between the pH value set using the pH indicator Q1 of FIG. These are examples of relational expressions F2a and F2b between the pH value set using the pH indicators Q2a and Q2b in FIG. These are examples of relational expressions F3a and F3b between the pH value set using the pH indicators Q3a and Q3b in FIG. Is an example of a relational expression F4 between the pH value set using the pH indicator Q4 of FIG. These are explanatory drawings of other examples of the chromaticity diagram M used in the present invention. These are explanatory drawings of still another example of the chromaticity diagram M used in the present invention. These are explanatory drawings of the relational expressions F9 and F10 between the pH value set using the chromaticity diagram M of FIGS. 9 and 10 and the deviation angle D. FIG. These are explanatory drawings of the conventional pH measurement system which calculates | requires the pH value of a culture medium from the color development of a pH indicator (phenol red).

  FIG. 1 shows an embodiment of the pH measuring device of the present invention applied to pH management of water quality such as factory water / drainage, agricultural water, rivers / lakes, aquariums / tanks and the like. The measuring device in the illustrated example includes a pH detection unit 10 and a pH measurement unit 20. The pH detection unit 10 includes a film 11 containing a pH indicator Q, a colorimeter 12 facing the film 11, and a holder 14 incorporating the film 11 and the colorimeter 12, and the holder 14 is at one end. By closing the provided opening with the film 11, the internal space can be made into a watertight structure in which water does not enter, and the colorimeter 12 is enclosed in the watertight internal space. It is desirable that the film 11 be appropriately exchangeable. Further, the holder 14 can be appropriately provided with an attachment portion, and can be of an immersion type in which the detection unit 12 is installed in water according to the measurement target T, or a flow-through type in which the detection unit 12 is attached to the inside of irrigation water or drainage piping. .

  An example of the film 11 containing the pH indicator Q in the illustrated example is a copolymer including a monomer component (pH indicator monomer) having a pH indicator portion and a polymerizable portion, as disclosed in Patent Document 4. The pH-indicating monomer has a molecular skeleton that can be protonated reversibly in water of a specific color change range, and is a monomer component (non-ionic monomer) having other appropriate electrically neutral sites and polymerizable sites. And a copolymer insoluble or hardly soluble in water. For example, a water-insoluble copolymer containing a pH indicator monomer and a nonionic monomer is formed into a film shape to form a film 11 so that the pH value of the water quality of the measurement target T can be continuously measured over a long period of time. Measurement device. However, in the present invention, the pH indicator Q is not limited to a film that is insoluble in water. For example, the pH indicator Q may be soluble or the pH indicator Q may be powdered. Further, in the present invention, it is possible to use a pH indicator Q such as phenol red belonging to the prior art, and even when such a pH indicator Q is used, a pH value measuring method in consideration of the entire color development as will be described later. By applying it, it is possible to expect the effect of expanding the measurement range of the pH value as compared with the prior art.

  Preferably, pH indicator Q is a monomer component (ionic) having an ionic moiety and a polymerizable moiety, as disclosed in Patent Document 4, together with a pH indicator monomer (including a nonionic polymer as required). Monomer). A copolymer containing an ionic monomer becomes a polyelectrolyte containing a charged group (dissociable functional group) in the side chain. For example, hydrogen ions gather in the vicinity of a segment derived from an anionic monomer in the copolymer. On the contrary, the vicinity of the segment derived from the cationic monomer is a region where the hydrogen ions repel (local dilution region). The color development of the pH indicator monomer in the copolymer shifts to the alkaline side when affected by the locally concentrated region, and shifts to the acidic side when affected by the locally diluted region. Therefore, by appropriately adjusting the mixing ratio of the pH indicator monomer (including nonionic polymer if necessary) and the ionic monomer, the color change range of the copolymer is changed from the color change range specific to the pH indicator site. It can be moved or expanded beyond the inherent color gamut. For example, it is assumed that the film 11 shown in the drawing is formed into a film of an insoluble copolymer in which the mixing ratio of the pH indicator monomer and the ionic monomer is adjusted so that the color change range corresponding to the measurement target T is obtained. Such copolymers and monomer components are described in detail in US Pat.

  An example of the colorimeter 12 in the illustrated example is a sensor that measures the color development of the film 11 including the pH indicator Q by facing the opposite side of the film 11 that contacts one side of the measurement object. For example, the colorimeter 12 is operated by supplying power from the pH measurement unit 20 via the signal / power cable 15, and a digital signal or an analog signal corresponding to the color of the film 11 is output to the colorimeter 12, and the output The signal is returned to the pH measuring unit 20 via the signal / power cable 15 to calculate the pH value. Although the color measuring unit 12 in the illustrated example is an integrated type adjacent to the film 11, for example, a light emitting unit / light receiving unit connected by an optical fiber or an optical rod or the like is included in the colorimeter 12, so that the light emitting unit / light receiving unit is included. Only the part can be adjacent to the film 11 and the colorimeter 12 can be installed at a remote location. Alternatively, instead of the colorimeter 12, a camera (not shown) that captures a color image of the film 11 is included in the pH detection unit 10, and the color image output from the camera is input to the pH measurement unit 20 to obtain a pH value. Can also be calculated.

  An example of the pH measurement unit 20 in the illustrated example is a computer having storage means 21 such as a primary storage device or a secondary storage device, an input device 22 such as a keyboard / mouse, and an output device 23 such as a display / printer. . The storage means 21 stores a chromaticity diagram M, a relational expression F, etc., which will be described later. Further, as an internal program, the operation means 24 for changing the settings of the chromaticity diagram M, the relational expression F, etc., and the output signal (or the color image of the camera) described above are input via the input device 22. A pH conversion unit 26 that measures the pH value of the measurement target T, and an output unit 25 that appropriately outputs the operation result of the operation unit 24 and the measurement result of the conversion unit 26 to the output device 23 are provided.

  FIG. 3 shows a flowchart of a method for measuring the pH value of the measuring object T by the measuring device of FIG. Hereinafter, the operation and function of the measuring apparatus of FIG. 1 will be described with reference to the flowchart of FIG. First, in step S101 of FIG. 3, the film 11 of the pH detecting unit 10 is brought into contact with a plurality of samples having different pH values (for example, aqueous solutions having different pH values, hereinafter referred to as pH samples) S1, S2,. The indicator Q is colored, and an output signal (or a color image of the camera) corresponding to the color of the pH indicator Q is input to the detecting means 27 of the converting means 26 of the measuring unit 20. The detecting means 27 plots the input output signal of the colorimeter 12 on a chromaticity diagram M in which the white point O is arranged at the center, and as shown in FIG. , The declination angles D1, D2,... Of the coloring points C1, C2,. The chromaticity diagram M used in step S101 can be stored in the storage unit 21 via the operation unit 24 in advance.

  An example of the chromaticity diagram M is a CIExy chromaticity diagram M1 as shown in FIG. In the xy chromaticity diagram M1 of FIG. 2, all colors are represented by two numerical values (x, y) = (X / (X + Y + Z), Y based on the stimulus values (X, Y, Z) of the three primary colors on the color specification. / (X + Y + Z)), and the detection means 27 can plot the color development indicated by the pH indicator Q as two color development points C (x, y). In addition, a white point O is arranged almost at the center of the xy chromaticity diagram M1, and by assuming a polar coordinate system centered on the white point O, two numerical values (x, y) of all colors can be obtained. It can be converted into the moving radius r and the deflection angle D. In the xy chromaticity diagram M1, the vividness increases toward the periphery from the central white point O and becomes a single light color at the peripheral boundary. Therefore, the converted radius r assuming the polar coordinates corresponds to the saturation of each color. , D can be considered to correspond to the degree of change (rate of change) in hue. In step S101, the detection means 27 plots the color development of the pH indicator Q on the chromaticity diagram M and detects the declination angle D, thereby determining the entire color development (hue) of the pH indicator Q as one numerical value (declination angle D). Convert to The radius r (saturation) of each color development point C can be changed by the concentration of the pH indicator Q included in the film 11.

However, in the present invention, the chromaticity diagram M is not limited to the CIExy chromaticity diagram M1, and as will be described later, the projection diagram M2 of the RBG color space (see FIG. 9) or the L ^* a ^* b ^* color space. It is also possible to convert the entire color of the pH indicator Q into one numerical value (deflection angle D) using the cross-sectional view M3 (see FIG. 10) or the like. In the chromaticity diagram M1 of FIG. 2, the Y axis on the central white point O is the starting line, and the angle formed by the line connecting the white point O with respect to each of the coloring points C1, C2,. Although D1, D2,... Are set, the setting of the start line is not limited to the illustrated example. For example, the declination D is detected using the X axis as the start line, or the declination D is detected using the line segment connecting the color point having the minimum pH value (or color point having the maximum pH value) with the white point O as the start line. May be.

After detecting the declination angles D1, D2,... Of the coloring points C1, C2,... Corresponding to the samples S1, S2,. Is set to a relational expression F between the pH values of the pH samples S1, S2,... And the declination angles D1, D2,. For example, as shown in FIG. 5, the pH values of the samples S1, S2,... Are set as independent variables, and the color development points C1, C2,. The relational expression can be obtained by regression analysis with the angles D1, D2,. A logarithmic model (logarithmic approximation) such as the following equation (1) can be used as the regression model, but the present inventor uses a logistic model (logistic regression curve) such as the equation (2). Thus, it has been found that a relational expression capable of accurately estimating the pH value from the declination angle D can be obtained regardless of the extent of the color change range of the pH indicator.
D = α · log (β · pH) + γ ... (1)
D = α / (1 + β · exp (−γ · pH)) (2)

[Experimental Example 1]
The mixing ratio of dimethylaminoazobenzene acrylate (AABAA), which is a pH indicator monomer, and N-isopropylacrylamide (NIPAAm), which is a nonionic monomer, is adjusted, and a cationic monomer (N, N, N) as necessary. -Trimethyl)-(2-acryloylethyl) -ammonium chloride (TMAEACl) was added while copolymerizing to prepare three types of pH indicators (gels) Q1, Q2a, and Q2b with different color development areas shown in Table 1. . The color development area of each pH indicator Q1, Q2a, Q2b is shown in FIG. In addition, instead of TMAEACl, 3-sulfopropyl acrylate potassium salt (SPAK), which is an anionic monomer, is added and copolymerized, so that two kinds of pHs having different color development ranges as shown in Table 1 and FIG. Indicators (gels) Q3a and Q3b were prepared. Furthermore, instead of AABAA, vinyl-2 ′, 4′dihydroxyazobenzene (VHA) was copolymerized with a nonionic monomer (NIPAAm) as a pH indicator monomer, whereby pH indicators in the color gamut shown in Table 1 and FIG. 4 ( Gel) Q4 was prepared.

Each of the six pH indicators Q1 to Q4 shown in Table 1 is dipped in an aqueous solution sample S having a different pH adjusted using hydrochloric acid, sodium hydroxide and pure, and each color is developed. (X-rite, Colormunki Photo), and the output signal of the colorimeter 12 corresponding to color development was plotted on the CIExy chromaticity diagram M1 shown in FIG. . Since the output signal of the colorimeter 12 is in the CIE L ^* a ^* b ^* format, the output signal is converted into the CIExy format and plotted on the chromaticity diagram M1. For each of the pH indicators Q1 to Q4, the line segment connecting the white point O with the color point having the smallest pH value (color point when brought into contact with the most acidic aqueous solution sample) is used as the starting line. Deviation angle D of the coloring point corresponding to other pH values was detected.

  FIG. 5A shows a CIExy chromaticity diagram M1 in which the coloring point C of the pH indicator Q1 immersed in different aqueous solution specimens S is plotted. A plurality of coloring points C having different pH values are arced around the white point O. It shows that it is lined up like drawing. FIG. 5B shows a relational expression F1 (α = 52.561, β = 13.830, γ = equation (2)) between the pH value of each coloring point approximated using the logistic model and the deviation angle D. 1.3583). A logistic model is generally known as a model that fits the relationship with the proportion y of individuals that respond to a certain stimulus x, such as the relationship between the dose of a poison and the mortality rate (Non-patent Document). 1). Relational expression 1 in FIG. 5B shows that the color change points C are accurately applied to the logistic regression curve F1 in a relatively wide color change range of pH = 0 to 6 and are approximated based on the logistic model. The expression F1 indicates that the pH value can be accurately estimated from the color of the pH indicator Q1.

  FIG. 6 shows a relational expression F2a obtained by approximating the relationship between the pH value of each aqueous solution sample S and the deviation angle D of the coloring point C when immersed in each aqueous solution sample S using the logistic model for the pH indicators Q2a and Q2b. , F2b. As can be seen from the comparison of the color development area of the pH indicators Q2a and Q2b and the color development area of the pH indicator Q1 in FIG. 4, the color development areas of the pH indicators Q2a and Q2b can be obtained by adding and copolymerizing a cationic monomer (TMAEACl). Can be moved to the acidic side from the non-added pH indicator Q1. The relational expressions F2a and F2b in FIG. 6 indicate that each color change point C is accurately applied to the logistic regression curves F2a and F2b even when the color development region moves to the acidic side, and the color change region of the pH indicator is wide and narrow. Regardless, the relational expressions F2a and F2b approximated based on the logistic model indicate that the pH value can be accurately estimated from the color of the pH indicators Q2a and Q2b.

  FIG. 7 shows the relational expressions F3a, Q3a, Q3b that approximate the relationship between the pH value of each aqueous solution sample S and the deviation angle D of the coloring point C immersed in each aqueous solution sample S using a logistic model. F3b is shown. As can be seen from the color development regions of the pH indicators Q3a and Q2b in FIG. 4, when an anionic monomer (SPAK) is added and copolymerized, the color change region can be moved or expanded to the alkaline side as the addition amount increases. . The relational expressions F3a and F3b in FIG. 7 indicate that each color change point C is accurately applied to the logistic regression curves F3a and F3b even when the color development range extends to the alkaline side. It is shown that the pH value can be accurately estimated from the color of the pH indicators Q3a and Q3b by the relational expressions F3a and F3b approximated based on

  Further, FIG. 8 shows a relational expression F4 that approximates the relationship between the pH value of each aqueous solution sample S and the deviation angle D of the coloring point C immersed in each aqueous solution sample S using the logistic model for the pH indicator Q4. As can be seen from the comparison between the color development range of the pH indicator Q4 and the color change range of the pH indicators Q1 to Q3 in FIG. 4, when the pH indicator monomer AABAA is used, the color change range is on the acidic side, whereas the pH indicator monomer VHA. When is used, the color change range is on the alkaline side. The relational expression F4 in FIG. 8 shows that even when the color development region moves to the alkaline side, each discoloration point C is accurately applied to the logistic regression curve F4, and from the color development of the pH indicator Q4 by the relational expression F4 approximated based on the logistic model. This means that the pH value can be estimated with high accuracy.

  Returning to the flowchart of FIG. 3, in step S <b> 103, the relational expression F of the pH indicator Q set by the setting unit 28 is stored in the storage unit 21. In step S104, it is determined whether or not there is another pH indicator Q for which the relational expression F should be set. If there is another pH indicator Q, the process returns to step S101 and the above-described steps S101 to S103 are repeated. For example, by repeating steps S101 to S103 while replacing the film 11 of the pH detection unit 10 with the film 11 containing the six types of pH indicators Q1 to Q4 shown in Table 1, the six types of relational expressions in FIGS. F1 to F4 can be set. If relational expressions F1 to F4 of pH indicators Q1 to Q4 having different color change ranges are stored in the storage unit 21, a wide range of pH values are measured using a combination of a plurality of pH indicators Q1 to Q4 as will be described later. be able to.

  Note that the setting process of the relational expression F in steps S101 to S104 described above is not necessarily performed at the pH measurement site, and can be set in advance using an appropriate pH sample S in a laboratory, for example. It is also possible to store the relational expression F in the storage unit 16 of the pH measuring unit 20. In this case, it suffices to provide a step of inputting the relational expression F to the pH measuring unit 20 instead of steps S101 to S104, and steps S101 to S104 for setting the relational expression F for each pH indicator Q can be omitted.

  Steps S105 to S107 in the flowchart of FIG. 3 show processing for measuring the pH value of the water quality of the measurement target T based on the relational expression F for each pH indicator Q stored in the storage unit 21. In step S105, if a plurality of relational expressions F of the pH indicator Q are stored in the storage unit 16, the pH indicator Q and the relational expression F used for measurement are selected as necessary. In step S106, the film 11 of the pH detector 10 is brought into contact with the measurement target T to develop the color of the pH indicator Q, and the output signal (or the color image of the camera) of the colorimeter 12 corresponding to the color development is converted by the conversion means 26. Input to the detecting means 27. Similarly to step S101 described above, the detecting means 27 plots the input output signal of the colorimeter 12 on a chromaticity diagram M in which the white point O is arranged at the center, and the white point O is on the polar coordinates at the center. The deviation angle Dt of the color development point Ct of the measurement target T is detected.

  In step S <b> 107, the deviation angle Dt of the coloring point Ct of the measurement target T is input to the calculation unit 29 of the conversion unit 26. The calculating unit 29 calculates the pH value of the measurement target T by applying the input declination Dt to the relational expression F (for example, the logistic model of the expression (2)). In step S108, it is determined whether or not the pH measurement is to be ended. If the measurement is to be continued, the process returns to step S105 and repeats steps S105 to S107 described above. For example, in water quality monitoring with a wide pH fluctuation range, by repeating steps S105 to S107 while replacing the film 11 of the pH detection unit 10 with pH indicators Q1 to Q4p in Table 1, the pH value over a wide range of the measurement target is measured. can do.

  According to the present invention, the color development of the pH indicator Q is detected by plotting the color development of the pH indicator Q on the chromaticity diagram M, detecting the deviation angle D of the color development point C, and estimating the pH value from the deviation angle D. The pH value can be estimated in consideration of the whole, and the measurement accuracy can be improved as compared with the case where the pH value is measured by a specific color being colored. In addition, as described above with reference to Table 1, the pH value can be measured from the color of the pH indicator Q regardless of the extent of the color change range of the pH indicator Q.

  Thus, the provision of “a pH measuring method and apparatus capable of estimating the pH value in consideration of the entire color development of the pH indicator”, which is the object of the present invention, can be achieved.

FIG. 9B shows another example of the chromaticity diagram M that can be used in the flowchart of FIG. The chromaticity diagram M2 in the illustrated example is a projection view in which the black point is viewed from the white point in the RBG color space shown in FIG. 9A. In the RGB space, all colors (R, G, B) are within the range of a cube surrounded by a red axis (R axis), a green axis (G axis), and a blue axis (B axis) represented by 255, respectively. expressed. By looking through the black point (0, 0, 0) from the white point (255, 255, 255) of the color space of the legislative body, a regular hexagon in which the white point O is arranged at the center as shown in FIG. Is obtained. In the projection diagram M2 in FIG. 5B, as in the xy chromaticity diagram M1 in FIG. 2, the color development (R, G, B) indicated by the pH indicator Q is converted by the equation (11) to obtain two numerical values. Can be plotted as the color development point C (x, y). Further, by assuming a polar coordinate system centered on the white point O, the two numerical values (x, y) can be converted into a radius vector r and a declination angle D. This declination D can be considered as a result of converting the entire color development (hue) of the pH indicator Q into one numerical value (declination D).
(X, y)
= (R−G / 2−B / 2, √3 / 2 · G−√3 / 2 · B) (11)

  FIG. 11 (A) plots the color development (output signal of the colorimeter 12) when immersed in each aqueous solution sample S on the chromaticity diagram M2 of FIG. 9 (B) for the pH indicator Q3a in Table 1 described above. Then, the deviation angle D of the coloring point C is detected, and the relational expression F9 approximating the relationship between the pH value of each aqueous solution specimen S and the deviation angle D of the coloring point C immersed in each aqueous solution specimen S using a logistic model. Indicates. Similar to the case of using the xy chromaticity diagram M1 in FIG. 2, the relational expression F9 in the figure shows that each discoloration point C is accurately applied to the logistic regression curve. That is, from this relational expression F9, as a chromaticity diagram for detecting the deviation angle D of the color development point C in steps S101 and S106 in FIG. 3, the RBG color space is viewed from the white point to the black point. It can be seen that the projection M2 can be used.

FIG. 10B shows still another example of the chromaticity diagram M that can be used in the flowchart of FIG. The chromaticity diagram M3 in the illustrated example is a cross-sectional view parallel to the a ^* b ^* plane of the L ^* a ^* b ^* color space shown in FIG. L ^* a ^* b ^* color space, three orthogonal axes as shown in FIG. 10 (A) ^{(L *} axis, ^{a *} axis, ^{b *} axis) origin can be considered as a sphere centered at, is the ^{L *} axis Corresponding to the brightness, the a ^* b ^* plane corresponds to the hue. By cutting the L ^* a ^* b ^* color space in parallel with the a ^* b ^* plane, a circular cross-sectional view M3 in which the white point O is arranged at the center is obtained as shown in FIG. In the cross-sectional view M3 of FIG. 5B, the color development of the pH indicator Q can be plotted as two numerical color development points C (a ^* , b ^* ), and the polar angle of the polar coordinate system centered on the white point O is shown. A numerical value h corresponding to D can be calculated by equation (12). This numerical value h is obtained by converting the entire color development (hue) of the pH indicator Q into one numerical value.
h = tan ⁻¹ (b ^* / a ^* ) ……………………………… (12)

FIG. 11B plots the color development (output signal of the colorimeter 12) when immersed in each aqueous solution sample S on the chromaticity diagram M3 of FIG. 10B for the pH indicator Q3a of Table 1 described above. Then, a numerical value h corresponding to the deviation angle D of the coloring point C is detected, and the relationship between the pH value of each aqueous solution sample S and the deviation angle D (numerical value h) of the coloring point C immersed in each aqueous solution sample S is logistically determined. The relational expression F10 approximated using the model is shown. The relational expression F10 in the figure is slightly worse than the case of using the xy chromaticity diagram M1 in FIG. 2 and the projection diagram M2 in FIG. 9B, but each discoloration point C is applied to the logistic regression curve. It is shown that. That is, from this relational expression F10, as a chromaticity diagram for detecting the deflection angle D of the coloring point C in steps S101 and S106 of FIG. 3, an L ^* a ^* b ^* color space as shown in FIG. It can be seen that a cross-sectional view M3 parallel to the a ^* b ^* plane can be used.

DESCRIPTION OF SYMBOLS 10 ... Detection part 11 ... Measurement film 12 ... Colorimetry apparatus 14 ... Holder 15 ... Signal / power cable 20 ... pH measurement part (computer) 21 ... Storage means 22 ... Input device 23 ... Output device 24 ... Operation means 25 ... Output means 26 ... pH conversion means 27 ... detection means 28 ... setting means 29 ... calculation means 41 ... dish 42 ... main body 43 ... medium 44 ... lid 46 ... illumination 47 ... mounting table 48 ... illumination control unit 49 ... color imaging device 49a ... lens 49b Image sensor 51 ... Imaging control unit 52 ... Computer 53 ... Display unit 54 ... Input device C ... Color development point D ... Deviation angle F ... Relational expression M ... Chromaticity diagram O ... White point Q ... pH indicator r ... Radial radius S ... pH specimen T ... Detection target

Claims (13)

Plotting the color development of each of the pH indicators brought into contact with specimens having different pHs on a chromaticity diagram in which the white point is located at the center, and detecting the declination D of the color development point on the polar coordinate centered on the white point, A relational expression between the pH value of each specimen and the deviation angle D of the color development point of the pH indicator brought into contact with each specimen is set, and the deviation of the color development point from the color development when the pH indicator is brought into contact with the measurement object. A pH measurement method in which the angle D is detected, and the pH value of the measurement target is calculated from the deviation angle D of the coloring point of the pH indicator brought into contact with the measurement target and the relational expression. 2. The pH measuring method according to claim 1, wherein a film containing the pH indicator is provided, and the deviation angle D of the coloring point is detected from the color of the film. 3. The pH measuring method according to claim 2, wherein a color image of the film is created and a deviation angle D of the coloring point is detected from the color image. 4. The measurement method according to claim 1, wherein the chromaticity diagram is a CIExy chromaticity diagram, a projection view in which a black point is viewed from a white point in an RBG color space, or a ^{* in an} L ^* a ^* b ^* color space ^. b ^* pH measurement method as a cross-sectional view parallel to the plane. 5. The measurement method according to claim 1, wherein the relational expression is set such that the pH value of each sample is an independent variable, and the deviation angle D of the coloring point of the pH indicator brought into contact with each sample is a dependent variable. A pH measurement method as a logistic regression curve. 6. The measurement method according to claim 1, wherein the pH indicator comprises a monomer component having a pH indicating site and a polymerizable site, and a monomer component having an ionic site and a polymerizable site. A pH measurement method as a polymer. a detecting means for inputting a coloring signal of a pH indicator and plotting the coloring on a chromaticity diagram in which a white point is arranged at the center to detect a deviation angle D of the coloring point on a polar coordinate centered on the white point; pH Storage means for storing a relational expression between a pH value of a specimen having a different pH and a deviation angle D of the color development point of the pH indicator brought into contact with each specimen, and the color development point when the pH indicator is brought into contact with the measurement object A pH measuring device comprising a calculating means for calculating the pH value of the measurement object from the deviation angle D and the relational expression. 8. The measuring device according to claim 7, wherein the setting means sets the relational expression by inputting each pH value of the samples having different pH values and the deviation angle D of the coloring point of the pH indicator when brought into contact with each sample. A pH measuring device provided with 9. The pH measuring apparatus according to claim 7, wherein a film containing the pH indicator and a colorimeter facing the film are provided, and a color signal of the pH indicator is used as an output signal of the colorimeter. . 9. The pH measuring device according to claim 7, wherein a film containing the pH indicator and a camera for taking a color image of the film are provided, and a color signal of the pH indicator is used as the color image. 11. The measurement apparatus according to claim 7, wherein the chromaticity diagram is a CIExy chromaticity diagram, a projection view in which a black point is viewed from a white point in an RBG color space, or a ^{* in an} L ^* a ^* b ^* color space ^. b ^* pH measuring device as a cross-sectional view parallel to the plane. 12. The measurement apparatus according to claim 7, wherein the relational expression is set such that the pH value of each sample is an independent variable, and the deviation angle D of the coloring point of the pH indicator brought into contact with each sample is a dependent variable. A pH measurement device as a logistic regression curve. 13. The measuring device according to claim 7 , wherein the pH indicator comprises a monomer component having a pH indicating site and a polymerizable site, and a monomer component having an ionic site and a polymerizable site. A pH measuring device as a polymer.