JP5261848B2 - Electrochemical buffer capacity measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a buffering capacity measuring method which enables the shortening of an analyzing time and the reduction of an analyzing cost to be more safely and simply achieved by eliminating a problem in a conventional technique, and also to provide a buffering capacity measuring instrument. <P>SOLUTION: The buffering capacity measuring method is characterized by calculating the buffering capacity of a sample solution on the basis of the change of the pH of the sample solution with the elapse of time accompanied by the constant current electrolysis of the sample solution and the buffering capacity measuring instrument characterized by quantitatively continuing electrolysis using a constant current electrolytic device to measure the buffering capacity and calculating the intensity of taste. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

The present invention relates to a buffer capacity measuring device that detects the buffer capacity of a sample solution as the reciprocal of a change in pH over time.

The buffering action is an action that reduces the change in pH that occurs when an acid or alkali is added to the sample solution, and the buffering capacity indicates the magnitude thereof. A buffer capacity measuring method and apparatus for detecting the buffer capacity of a sample solution is disclosed in Japanese Patent Publication No. 63-002465. The method and apparatus for obtaining a buffer capacity by titrating an ionodiene-containing sample with a strong acid or a strong base. It has been known. In addition, the umami index includes measurement of the total nitrogen content, and the “Kjeldahl method”, the “Duma method” and the like are generally used.

However, the above-described buffer capacity measuring apparatus requires an acid for preparation of a sample, and further requires a strong acid or a strong base for titration. In addition, measurement of the total nitrogen content, which is an indicator of umami, takes a long time to analyze and the analysis cost is high.

On the other hand, unlike the above method, a taste recognition apparatus using a taste sensor as described in, for example, Japanese Patent No. 2578374 is conventionally known for measuring umami intensity. This taste recognition apparatus measures a potential change in response using a taste sensor using a polymer lipid membrane. These taste sensors are composed of a working electrode equipped with a polymer lipid membrane that responds to chemical substances and a reference electrode, and the potential response generated when the chemical substance is adsorbed to and desorbed from the polymer lipid film is used to obtain sample taste information. It is characterized by. This measurement method has the feature that taste can be measured without being influenced by the chemical components of the sample solution, but the durability of the polymer lipid membrane and the use of acids and bases in the washing process In addition, since a plurality of measurement steps are required, there is a problem that the apparatus is complicated and large, and the apparatus price is not affordable.

Japanese Patent Publication No. 63-002465 Japanese Patent No. 2578374

An object of the present invention is to provide a method for measuring buffer capacity in a simple and short time without using dangerous reagents such as acids and bases, and a buffer capacity measuring apparatus using the same.

The present invention has been made in view of the above circumstances, and its object is to solve the above-mentioned problems in the prior art, and to provide a buffer capacity capable of reducing analysis time and analysis cost more safely and easily. It is to provide a measuring method and a buffer capacity measuring device.

An object of the present invention is to provide a buffer capacity measuring method characterized by performing constant current electrolysis on a sample solution and calculating the buffer capacity of the sample solution based on the change over time of the pH of the sample solution. This is achieved by a buffer capacity measuring device characterized in that, by using a current electrolyzer, electrolysis can be quantitatively continued to measure the buffer capacity and the umami strength can be calculated.

As described above, according to the present invention, the buffer capacity can be measured easily and in a short time without using an acid or alkali, and a buffer capacity measuring apparatus using the same is provided. Thereby, umami intensity can be calculated easily and in a short time.

In order to solve the above-mentioned problems, the buffer capacity measuring method according to the present invention injects a sample solution diluted with an electrolyte solution or the electrolyte solution into a measurement cell separated by a cation exchange membrane, and a working electrode on the sample solution side. In addition, a counter electrode is inserted into the electrolyte solution side of the pH electrode, and a predetermined current is applied to the working electrode and the counter electrode using a constant current electrolysis apparatus. The buffer capacity measuring method is characterized in that the buffer capacity is obtained by the following steps [1] to [3].

[1] A step of setting an applied current from a state in which no current is applied to both the working electrode and the counter electrode. [2] A step of measuring and recording a change in pH over time by the current operation with a pH meter. [3] A step of calculating a buffer capacity from the change in pH with time.

By using both positive and negative applied currents for the sample, the buffer capacity in a wide range of pH can be measured.

In the first operation, electrolysis based on the following reaction formulas (1) and (2) occurs.

(Formula 1)
Anode: 2H ₂ O → O ₂ + 4H ⁺ + 4e ⁻ (1)
(Formula 2)
Cathode: 4H ₂ O + 4e ⁻ → 2H ₂ + 4OH ⁻ (2)

By constant current electrolysis, the water on the anode side is oxidized to generate oxygen, release electrons, and the pH changes to acidic (1). The sample solution on the cathode side is reduced to generate hydroxide ions (OH ⁻ ), and the pH changes to basic (2). Measure the pH on the sample side with a pH meter and record the change in pH over time.

Based on the electrolysis law of the following reaction formula (3), H and OH ⁻ generation amounts per hour at the anode and the cathode can be calculated.

(Formula 3)
m = (I * t / F) * (M / z) (3)
(Where m is the mass of the changed substance, I is the current value, t is the electrolysis time, F is the Faraday constant, M is the molar mass of the substance, and z is the number of electrons)

The buffer capacity is determined by using the reciprocal of pH change with time (dt / dpH) from the change with time of pH.

As shown in FIGS. 1 to 4, the buffer capacity curve plotted with the buffer capacity on the vertical axis, the pH on the horizontal axis, and (1) about pH as described in Japanese Patent Publication No. 63-2465. A buffer capacity band near 4 is observed, (2) a buffer capacity band near pH 9.5, and (3) a weak buffer capacity band near pH 7 is observed. The buffer capacity bands of (1) and (2) reflect the type and amount of amino acids such as glutamic acid and aspartic acid contained. Therefore, the buffer capacity is an index of umami such as fermented food.

In the present invention, the buffer capacity is compared with the measurement result of the taste sensor, and the buffer capacity is used as an umami index by obtaining the correlation between the buffer capacity and the umami intensity.

For example, a commercially available taste recognition device is used as the taste sensor. As the taste recognition device, a membrane potential measurement type sensor using a polymer lipid membrane that responds to taste components can be used. For example, SA402B manufactured by Intelligent Sensor Technology is used.

The present inventor considered the relationship between the buffer capacity required by the buffer capacity measurement method and the umami intensity required by the taste recognition device, and as shown in FIGS. (Relationship) was established.

As shown schematically in FIG. 9, the basic structure of the buffer capacity measuring device of the present invention is a measurement cell separated by a cation exchange membrane into an anode chamber and a cathode chamber, a computer, a constant current electrolysis device, It consists of a pH meter.

The working electrode and each counter electrode are connected to a constant current electrolysis device that functions as an applied current control device. The constant current electrolysis device is a device useful for electrochemical measurement, and can control the current flowing from the working electrode to the counter electrode to an arbitrary value.

The cation exchange membrane product itself used in the present invention may be a known product, for example, commercially available from Asahi Glass Co., Ltd. under the trade name of Selemion. These films usually have a film thickness of 130 to 400 μm, and can be appropriately selected according to the intended durability.

By using the cation exchange membrane, the anode chamber and the cathode chamber are separated, and only cations that are excessive in the sample solution can be moved to the cathode side using the cation exchange membrane.

The measurement cell is made of, for example, an acrylic resin that is inexpensive and easy to clean.

The volume of the measurement cell and the volume of the sample solution to be injected are not limited, but 50 cc or less is preferable. Of these, about 5 cc is preferably used. When the capacity exceeds 50 cc, the measurement time becomes long, and furthermore, the applied current value must be increased to shorten the measurement time, which is not economically preferable.

In the measurement cell, a working electrode and a counter electrode arranged opposite to each other with a cation exchange membrane interposed are inserted, and a pH electrode is inserted into the anode chamber or the cathode chamber.

In the present invention, the anode chamber and the cathode chamber during measurement are preferably stirred. For example, a magnetic stirrer or the like can be used. Thereby, since the distribution state of the electrolyte in the anode chamber and the cathode chamber is made uniform, an accurate pH can be detected.

The applied current value in the present invention is suitably from 0.01 A to 1 A and from -0.01 A to -1 A, and among these, 0.3 A and -0.3 A are preferably used. As shown in FIG. 11, when the applied current value is less than 0.01 A and exceeds −0.01, the measurement time becomes long, and the action as a rapid measurement device becomes insufficient. When the value exceeds 1A or less than -1A, the measurement time becomes extremely short, and is not suitable for accurate measurement.

The applied current values of 0.01A to 1A and -0.01A to -1A are the opposite directions of the current, but the reactions shown in the reaction formulas (1) and (2) are the same. .

The measurement time in the present invention can be adjusted by manipulating the amount of the sample solution and the applied current value, but is usually preferably about 1 to 15 minutes, more preferably about 2 to 5 minutes. Moreover, when it exceeds 15 minutes, it is not suitable as a quick measuring apparatus.

In the present invention, the working electrode and the counter electrode are both made of platinum. That is, an inactive electrode is used as the working electrode, and the electrode substance itself does not cause a reaction such as oxidative elution, and can only transfer electrons to the substance in the solution during the electrode reaction.

The working electrode is preferably platinum, but other than that, for example, gold, glassy carbon, or the like can be used.

The computer is a device for analyzing the obtained pH data and calculating the buffer capacity (dt / dpH).

As the pH meter used in the present invention, for example, a pH meter model number F-54 commercially available from HORIBA, Ltd. is used. The pH meter is connected to a computer that functions as an analysis device.

The supporting electrolyte used for the electrolyte solution is Na ₂ SO ₄ .

Moreover, KNO ₃ etc. can also be used as a supporting electrolyte.

The dilution ratio of the sample solution is suitably 1 to 500 times. In many foods, when the dilution ratio in the electrolyte solution is low, the non-electrolyte in the food interferes with the measurement, and when it exceeds 500 times, the buffer capacity component becomes diluted and is not suitable for accurate measurement. . As shown in FIG. 12, the general food is preferably diluted 2 to 100 times with the electrolyte solution, and more preferably 5 to 50 times.

The sample preparation method is as shown in FIG.
.

Several foods were subjected to measurement tests using the buffer capacity measuring apparatus of the present invention produced above. In the measurement, a 1 molar Na ₂ SO ₄ solution was used as an electrolyte solution, and +0.3 A and −0.3 A were applied to a 50 cc sample solution. Examples of the buffer capacity curves of some foods are shown in FIGS. 1-4, and graphs showing the relationship between the buffer capacity (dt / dpH) and umami strength of some foods are shown in FIGS. (FIGS. 1 and 5) Amino acid, 50-fold dilution, (FIGS. 2 and 6) Soy sauce, 50-fold dilution, (FIGS. 3 and 7) Japanese sake, 5-fold dilution, (FIGS. 4 and 8) Miso, 5-fold dilution

1 to 8, it can be seen that the buffer capacity can be measured easily and in a short time without using an acid or an alkali, and the umami strength using the same can be calculated.

FIG. 1 is a buffer capacity curve showing the relationship between the buffer capacity (dt / dpH) and pH of several amino acids. FIG. 2 is a buffer capacity curve showing the relationship between the buffer capacity (dt / dpH) and pH of several soy sauces. FIG. 3 is a buffer capacity curve showing the relationship between the buffer capacity (dt / dpH) and pH of several sakes. FIG. 4 is a buffer capacity curve showing the relationship between the buffer capacity (dt / dpH) and pH of several miso. 1 to 4 are buffer capacity curves in which buffer capacity (dt / dpH) is plotted on the vertical axis and pH is plotted on the horizontal axis for several foods. FIG. 5 is a graph showing the relationship between the buffering capacity (dt / dpH) of several amino acids and umami strength. FIG. 6 is a graph showing the relationship between the buffer capacity (dt / dpH) and umami strength of several soy sauces. FIG. 7 is a graph showing the relationship between the buffer capacity (dt / dpH) and umami strength of several sakes. FIG. 8 is a graph showing the relationship between the buffer capacity (dt / dpH) and umami strength of several miso. FIGS. 5 to 8 plot the buffer capacity (dt / dpH) on the vertical axis and the umami strength on the horizontal axis for several foods. It is a graph which shows the relationship between dt / dpH) and umami intensity. FIG. 9 is a diagram schematically showing the basic structure of the buffer capacity measuring device of the present invention. FIG. 10 shows a general method for preparing a sample solution. FIG. 11 is a graph showing the relationship between the buffer capacity measurement time and the applied current value, in which the buffer capacity measurement time of the 1 molar Na ₂ SO ₄ solution is plotted on the vertical axis and the logarithm of the applied current value is plotted on the horizontal axis. FIG. 12 is a graph showing the relationship between buffer capacity (dt / dpH) and dilution ratio, with the buffer capacity (dt / dpH) of concentrated soy sauce plotted on the vertical axis and the logarithm of dilution ratio plotted on the horizontal axis.

1 Working electrode 2 Counter electrode
3 Constant current electrolyzer
4 pH meter
5 Measurement cell
6 Computer
7 Cation exchange membrane 8 Na ₂ SO ₄ solution 9 Sample solution

Claims (3)

A measurement cell that contains the sample solution, a cation exchange membrane that isolates the measurement cell into an anode chamber and a cathode chamber, a pH meter that monitors the pH of the sample solution, and an electric current applied to the sample solution in the measurement cell Buffer capacity characterized by having a constant-current electrolysis apparatus to be supplied and a processing mechanism for measuring the pH change of the sample solution and calculating the reciprocal of the change in pH over time as the buffer capacity of the sample solution from the result measuring device. 2. The buffer capacity measuring apparatus according to claim 1, wherein the dilution ratio of the sample solution with the electrolyte solution is 1 to 500 times. 2. The buffer capacity measuring device according to claim 1, wherein an applied current value of the constant current electrolysis device is ± 0.01 A to ± 1 A.