JPH0448187B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to the pH control of various solutions, such as solutions used for medical purposes, general chemistry, biochemistry, food, etc.
and a measuring device for precisely measuring ion concentration.

(Prior Art) Conventionally, the pH and ion concentration of a solution have been measured by, for example, immersing a composite electrode 100 as shown in FIG. 6 in a measurement solution 111.
The composite electrode 100 fills the glass support tube 103 with an internal liquid 102 and divides the glass support tube 103 into a chamber A located from the bottom to the center and around the glass support tube 103 using a partition plate. An indicator electrode (glass electrode or ion electrode) 101 formed by dividing into chamber B and arranging an internal electrode in chamber A, and a comparison electrode 10 arranged in chamber B.
6, a liquid junction 104 that causes the internal liquid 102 in chamber B to flow out into the measurement solution 111, and
2 is provided with a replenishment hole 105 for replenishing.

According to the measuring device, mobile ions are exchanged in the glass membrane below the indicator electrode 101 and are sensitive to ions in the measurement solution, so that the indicator electrode
A closed circuit is formed between the reference electrode 106 and the comparison electrode 106, and a potential difference is generated between the two electrodes. This potential difference is amplified by a high input amplifier 107 and an analog indicator 108
It was displayed as a voltage value or a PH value converted from a voltage value. Alternatively, the output signal of the high input anti-amplifier 107 is processed by the digital processing circuit 109, and the PH value of the measurement solution is displayed on the digital display.

(Problems to be Solved by the Invention) According to the above measuring device, in order to accurately measure the pH and ion concentration of the measurement solution, the reference electrode 106 is required to be as insensitive to all ions as possible. That is, ideally, the reference electrode 106 should have a constant potential regardless of the measurement solution.

However, according to the measuring device described above, a liquid junction potential is generated at a portion where the internal liquid 102 comes into contact with the measurement solution 111 through the liquid junction portion 104, so that the potential of the comparison electrode 106 fluctuates. The liquid junction potential tends to increase as the concentration of the measurement solution 111 increases (for example, the acidity increases as the molar concentration of hydrogen ions increases (the PH value, which is the hydrogen index, decreases)).

A specific measurement example will be described with reference to FIG. 4. First, the hydrogen index is PH6.863 at 25℃
A neutral phosphate standard solution with a hydrogen index of PH
Perform standard calibration of the measuring device by setting the PH values (PH6.863, PH4.004) corresponding to the voltages (8.014mV, 177.231mV) generated by each standard solution using a phthalate standard solution of 4.004. Do this. After that, when measuring an oxalate standard solution with a hydrogen index of PH1.679 at 25℃, an error potential of several mV was generated on the + side of the voltage value (314.769) that should be generated in this standard solution, so the error could be corrected. The PH value corresponding to the included voltage (PH value displayed on the measuring device) is the original PH value
It is displayed as a larger value than 1.679 with an error of 0.04 to 0.06.

This phenomenon can be expressed as follows.
The potential difference generated between the indicator electrode 101 and the comparison electrode 106 is the potential difference E, the potential of the indicator electrode 101 (independent potential of the internal electrode + potential of the glass membrane) is the potential G, and the potential of the comparison electrode 106 (independent potential of the internal electrode + liquid junction) When the potential) is the potential J, E=G+J...(1) holds true. The potential G of the indicator electrode 101 changes approximately linearly with the PH value of the measurement solution, but the potential J of the reference electrode 106 increases as the concentration of the measurement solution increases due to the presence of the liquid junction 104. . Therefore, the error in the potential difference E between the indicator electrode 101 and the comparison electrode 106 also increases as the concentration of the measurement solution increases.

The present invention was made in view of the above circumstances, and
The object of the present invention is to provide a measurement device that can accurately measure pH and ion concentration without being affected by the concentration of the measurement solution.

(Means for Solving the Problems) In order to solve the above-mentioned conventional drawbacks, the PH and ion concentration measuring device of the present invention includes an indicator electrode sensitive to ions in a test solution, a first comparison electrode, and a second comparison electrode. a reference electrode provided with a reference electrode, voltage detection means for detecting electromotive force between the first comparative electrode and the second electrode, and the indicator electrode, respectively, and a reference potential regulator that obtains a reference potential of the reference electrode from each of the electromotive forces; It is configured with the following.

The first comparison electrode includes an internal electrode immersed in an internal liquid and a liquid junction.

The second comparison electrode includes an internal electrode immersed in an internal liquid and a carbon diaphragm interposed between the internal liquid and the test solution.

(Function) According to the present invention, since the diaphragm provided on the second comparison electrode is made of carbon, the second electromotive force generated between the second comparison electrode and the indicator electrode is transferred between the second comparison electrode and the indicator electrode. The polarity of the first electromotive force generated between the first electromotive force and the electrode can be made different. Therefore, each electromotive force is detected by a voltage detection means, and a reference potential of a reference electrode is obtained from each electromotive force in a reference potential regulator,
By measuring the potential difference between this reference potential and the indicator electrode, it is possible to eliminate measurement voltage errors that vary with changes in the concentration of the measurement solution due to the presence of the liquid junction of the first comparison electrode.

The above phenomenon will be explained with reference to FIG. The first comparison electrode of the present invention is the comparison electrode 10 in the conventional example.
6, the potential difference E is the potential difference that occurs between the indicator electrode and the first comparison electrode, and the potential J is the first comparison electrode potential (independent potential of the internal electrode + liquid junction potential). Further, the potential G is the potential of the indicator electrode (single potential of the internal electrode+potential of the glass membrane), as in the conventional example. Then, the potential difference generated between the indicator electrode and the second comparison electrode is the potential difference E', and the potential of the second comparison electrode (internal electrode independent potential + diaphragm potential) is the potential difference C.
Then, the potential difference E′ satisfies the following equation.

E'=GC...(2) From equations (1) and (2), E−E′=(G+J)−(GC)=J+C……(3) becomes.

In equation (3), J+C is the sum of the potentials generated at the first comparison electrode and the second comparison electrode, that is, the value of the error potential. Therefore, if J and C have the same absolute value and opposite polarities, J+C becomes 0, and the error potential can be removed. According to the present invention, by using a carbon diaphragm, the potential J of the first comparison electrode is
and the potential C of the second comparison electrode can be reversed in polarity, and even if the absolute values of the potential J and the potential C are different, they can be adjusted by a reference potential regulator so that J+C becomes 0. A reference potential is set.

By setting the reference potential so that J+C is 0, and calculating E+E', E+E'=(G+J)+(G-C)=2G...(4), which is the ideal electromotive force generated at the indicator electrode. You can get twice the value.

(Example) An example of the present invention will be described with reference to the drawings.

As shown in FIG. 2, the PH and ion concentration measuring device according to the present invention includes a reference electrode 1 and an indicator electrode 20 that is sensitive to ions in a test solution. The indicator electrode 20 is, for example, the composite electrode 1 shown in FIG.
Similar to the indicator electrode 101 of No. 00, the internal electrode is arranged in an internal solution (standard solution of PH 7.00) filled in a glass support tube, and mobile ions are generated in the glass membrane 20a at the bottom of the indicator electrode 20. is exchanged to make it sensitive to ions in the measurement solution.

As shown in the detailed configuration diagram in FIG. 1, the reference electrode 1 has a support tube 2 divided into two chambers by a partition plate 3 to form a first comparison electrode 1A and a second comparison electrode 1b. . The first comparison electrode 1a is filled with an internal liquid 4, and is provided with a replenishment hole 5 above the support tube 2 for replenishing the internal liquid 4, so that the internal liquid 4 flows out to the lower surface of the support tube 2. A liquid junction portion 6 is provided. In addition, a support plate 1 fixedly installed on the upper part of the support tube 2
An internal electrode 7 (for example, a silver-silver chloride electrode) is disposed such that one end is fixed to 0 and the other end is immersed in the internal liquid 4. The potential generated at internal electrode 7 is connected to reference electrode lead wire 9 via lead wire 8 .

The inside of the second comparison electrode 1b is filled with an internal solution 14 (preferably a medium (PH7.00) standard solution similar to the internal solution of the indicator electrode 20). Further, an internal electrode 15 is arranged such that one end thereof is fixed to a support plate 10 fixedly installed on the upper part of the support tube 2, and the other end side is immersed in the internal liquid 14. An opening 11 is bored in the lower side of the support tube 2, and a carbon diaphragm 12 is fixedly attached to the opening 11 so as to be covered with a heat-shrinkable tube 13, and the internal liquid 14 flows out of the support tube 2. I try not to let it happen. Further, an opening 16 is provided on the opposite side of the heat-shrinkable tube 13 facing the opening 11, and a reference electrode 16 is placed in the test solution 19 in the measurement atmosphere 18 as shown in FIG.
When (the support tube 2) is arranged, a diaphragm 12 is interposed between the test solution 19 and the internal liquid 14. The potential generated in the internal liquid 15 is connected to the reference electrode lead wire 9 via the lead wire 17, similarly to the internal electrode 7 of the first comparison electrode 1a.

Next, carbon diaphragm 1 used in the device of the present invention
The manufacturing method No. 2 will be explained. The carbon film is based on the patent application No. 59-102506, which was previously proposed by the applicant.
(Japanese Unexamined Patent Publication No. 60-247150), the manufacturing method thereof will be explained below.

As a first step for producing a carbon film to be used as the diaphragm 12 of the second comparative electrode 1a constituting the reference electrode 1 of the device of the present invention, first, commercially available graphite such as graphoil is mixed with 1 part of perchloric acid and 1 part of nitric acid. With a mixed acid containing 3 parts (HNO ₃ ) and 3 parts water,
Although there is no particular limitation, it is preferable to boil for 2 to 3 hours, then thoroughly stir and wash with water to form a slurry.

Next, an equal volume of carbon tetrachloride (CCl ₄ ) was added to this muddy graphite, placed in a quartz boat, and a mixed gas of 1 volume of chlorine (Cl ₂ ) gas and 10 volumes of nitrogen (N ₂ ) gas was added. While passing the graphite,
Although there is no particular limitation, heating is preferably performed at about 500°C for about 2 to 3 hours. After this heating, nitrogen gas is passed through and the heating temperature is further raised, preferably at 700 to 900℃ for 5 to 20 minutes, although there is no need to limit it in particular.
After heating for a minute, the mixture is cooled to obtain fine carbon powder, thereby completing the first step.

Next, in the second step, a chemically resistant, heat resistant, waterproof plastic powder such as Teflon (registered trademark) powder or propylene hexafluoride is added to the fine carbon powder obtained in the first step in a particularly limited manner. Although it is not necessary to do so, it is preferable to mix 5 to 10%, and roll press this mixture at a temperature of room temperature to 300°C, or press it into a mold to form it to a predetermined thickness, and then cool it to obtain a carbon sheet. to complete the second step.

The third step is a step of forming the carbon sheet obtained in the second step into a carbon electrode for a comparison electrode. That is, the two carbon sheets obtained in the second step were each used as poles, and the
DC electrolysis is performed in dilute acid (H ₂ SO ₄ ) at 100 μA to 2 mA/cm ² , although there is no particular limitation. The polarity is switched every 5 to 10 minutes, and DC electrolysis is performed under the same conditions. The solution is repeated 2 to 10 times, and then washed with water to clean and activate the surface, forming a carbon membrane.

Carbon diaphragm 12 manufactured as described above
is hardly sensitive to the pH value of the test solution 19, and according to the second comparison electrode 1b using this carbon diaphragm 12, the polarity is lower than that of an electrode with a conventional structure, for example, the first comparison electrode 1a. give rise to different potentials. Although the mechanism by which potentials with different polarities occur is not clear, this phenomenon has been confirmed through experiments. Therefore, the polarities of the electromotive force generated in the indicator electrode 20, the first comparison electrode 1a, and the second comparison electrode 1b have a relationship as shown in FIG.

The potential generated at the first comparison electrode 1a and the potential generated at the second comparison electrode 1b are inputted via the reference electrode lead wire 9 to a reference potential regulator 22 composed of a potentiometer. As described above, each potential has opposite polarity, so by changing the resistance value by adjusting the slider 22' in the reference potential adjustment 22, the reference potential (zero potential) that becomes the potential neutral point
can be found. The reference potential output from the reference potential regulator 22 is input to the high input anti-amplifier 21 via the PH value neutral side regulator 23. The PH value neutral side adjuster 23 is configured by a combination of a direct power supply 23' and a potentiometer, and when using a neutral standard solution during standard calibration, the PH value neutral side adjuster 23 adjusts the value displayed on the PH value display 24, which will be described later. This is for setting (zero adjustment).

The high input anti-amplifier 21 inputs the output from the indicator electrode 20 and the reference potential, outputs the voltage value generated in the test solution 19, and calculates the PH value corresponding to the voltage value.
A PH value display 24 provides digital display. Further, 25 is a feedback resistor (PH value acidic side adjuster) for making a part of the output of the high input anti-amplifier 21 negative, and by adjusting this resistance value, the amplification degree of the high input anti-amplifier 21 can be adjusted. You can correct the PH value by adjusting it. This adjustment is performed when using an acidic standard solution during standard calibration.
This is performed as a setting (zero adjustment) of the display value of the value display 24.

Further, a stirring bar 26 is installed on the bottom surface of the measurement container 18, and the stirring bar 26 is configured to be rotatable by a stirrer 27.

Next, a method for measuring the PH value of a test solution using the above measuring device will be explained.

First, a neutral phosphate standard solution of PH6.863 and PH
Perform standard calibration on the neutral side and acidic side using 4.004 phthalate standard solution. At this time, the slider 22' of the reference potential regulator 22 is set at the center position so that the sum of the potentials generated by the first comparison electrode 1a and the second comparison electrode 1b becomes the reference potential, that is, on the neutral side. PH6.863 (25
℃) is put into the measurement container 18 as the test solution 19, and after inserting the indicator electrode 20 and the reference electrode 1, the stirrer 26 is rotated by the stirrer 27 to make the test solution 19. Stir. The generated electromotive force in this state is adjusted to a value displayed on the PH value display 24 by the PH value neutral regulator 23 to 6.863.

Next, as a standard calibration on the acidic side, test solution 19 was added.
After replacing the phthalate standard solution with PH4.004 (25℃) and stirring in the same manner as above, the electromotive force in this state is adjusted by the feedback resistor (PH value acidic side regulator) 25 to adjust the PH value table device 24. Adjust the display value to 4.004.
Standard calibration is completed with the above operations.

Subsequently, the test solution 19 is replaced with the oxalate standard solution and measured. At this time, the electromotive force generated between the indicator electrode 20 and the first comparison electrode 1a has an error potential due to the liquid junction potential. According to the measuring device of this embodiment, the error potential can be measured by using the carbon diaphragm 12 at the second comparison electrode 1b.
A reference potential (zero potential) can be obtained by further canceling out the potential generated in The PH value corresponding to the electromotive force can be accurately displayed on the PH value display 24.

That is, in FIG. 4, the first comparison electrode 1a
If the potential C and the potential C of the second comparison electrode 1b have the same absolute value and different polarities, the slider 22' of the reference potential regulator 22 is set to the center position to output a zero potential. be able to. Furthermore, if the absolute values of the potential J of the first comparison electrode 1a and the potential C of the second comparison electrode 1b are different, for example, by moving the slider 22', When the potential J is twice the potential C of the second comparison electrode 1b, the slider 22' is placed 1/3 on the potential side of the second comparison electrode 1b and 2/3 on the first comparison electrode 1a side. If the position is set to , the output of the reference potential regulator 22 can be set to zero potential.

Therefore, of course, if the PH value is between 4.004 and 1.679,
Even if the value increases, errors caused by the reference electrode 1 can be prevented, and the indicator electrode 20 can accurately measure the PH value of the test solution 18.

In the above embodiment, the explanation has been given to canceling the error potential generated when the test solution 19 is on the acidic side, but the electromotive force on the alkaline side can also be corrected in the same manner.

FIG. 3 shows another embodiment of the present invention, in which parts having the same configuration as in FIG. 2 are designated by the same reference numerals. The different configurations will be mainly explained below.

In this embodiment, the indicator electrode 20 and the first and second comparison electrodes of the reference electrode 1 are connected to a high input anti-amplifier 28, respectively, and the high input anti-amplifier 28
In the storage device 29 connected to the reference electrode 1
A first electromotive force generated between the first comparison electrode of the reference electrode 1 and the indicator electrode 20 and a second electromotive force generated between the second comparison electrode of the reference electrode 1 and the indicator electrode 20 are respectively stored. The calculator 30 corrects the data stored in the storage device 29, and calculates the reference potential of the reference electrode 1 from each electromotive force data. The command device 31 is for commanding the calculation method in the calculator 30. The output of the storage device 29 passes through a converter 32 for converting the output value into a PH value corresponding to the output value, and a PH value display 33 displays the PH value of the test solution.

A method for measuring the PH value of a test solution according to this example will be explained. In addition, in FIG. 3, the PH value neutral regulator and the feedback resistor are omitted.

First, in the same manner as in the first example, PH6.863
Perform standard calibration on the neutral side and acidic side using a neutral phosphate standard solution of PH4.004 and a phthalate standard solution of PH4.004. The electromotive force is passed through a high-input anti-amplifier 28, and its output is stored as data in a storage device 29. The data is led to the calculator 30, and the electromotive force per 1 PH (mV/PH) is calculated, and the electromotive force value G _1.679 corresponding to 1.679, which is the PH value of the oxalate standard solution, is determined.

Subsequently, test solution 19 was diluted with oxalate standard solution (PH
1.679) and measure. If the electromotive force measured by the indicator electrode 20 and the first comparison electrode 1a at this time is E _1.679 , E _1.679 = (G + J) _1.679 ... (5) In addition, the second comparison electrode 1b equipped with the diaphragm 12 and the indicator electrode The electromotive force between 20 and 20 is E' _1.679 .

E′ _1.679 = (G-J) _1.679 ...(6) E′ _1.679 −E′ _1.679 = (J+C) _1.679 ...(7) Therefore, the reference electrode in the oxalate standard solution (PH1.679) The potential J and potential C that cause an error of 1 are found. If the potential J and the potential C are known, the ratio thereof is also known, so it is possible to calculate N that satisfies J=NC.If the calculator 30 calculates based on the command from the command unit 31 based on this value, the reference electrode 1
The reference potential of can be set to zero. As a result, E+E'=(G+J)+(G-NC)=2G...(8) can be satisfied, and a signal corrected to remove the error potential can be output from the storage device 29. . Then, the PH value is displayed on the PH value display 33 via the output-PH value converter 32 based on the corrected electromotive force value.

(Effects of the Invention) According to the present invention, the reference electrode is provided with a first comparison electrode having a liquid junction and a second comparison electrode having a diaphragm, and the diaphragm is made of carbon. A second comparison electrode generated between the first comparison electrode and the indicator electrode has a different polarity with respect to the first electromotive force generated between the first comparison electrode and the indicator electrode, and each electromotive force is detected by a voltage detection means. Since a reference potential is set by this method and the potential difference between this reference potential and the indicator electrode is measured, there is no measurement voltage error that fluctuates with changes in the concentration of the measurement solution due to the presence of the liquid junction of the first reference electrode. can be removed, making it possible to perform precise and stable measurements.

[Brief explanation of the drawing]

FIG. 1 is an explanatory cross-sectional view of a reference electrode constituting the measuring device of the present invention, FIG. 2 is an explanatory diagram of the configuration of one embodiment of the measuring device of the present invention, and FIG. 3 is an explanatory diagram of another embodiment of the present invention. Figure 4 is a graph showing the electromotive force between the indicator electrode and the first comparison electrode, the electromotive force between the indicator electrode and the second comparison electrode, and the value of ideal electromotive force without error. FIG. 6 is an explanatory diagram showing the directions of electromotive force of the electrode, the first comparison electrode, and the second comparison electrode, and FIG. 6 is an explanatory diagram of the configuration of a conventional PH and ion concentration measuring device. 1... Reference electrode, 1a... First comparison electrode, 1b
... Second comparison electrode, 4 ... Internal liquid, 6 ... Liquid junction, 7 ... Internal electrode, 12 ... Diaphragm, 19 ... Test solution, 20 ... Indicator electrode, 22 ... Reference potential adjustment Instrument, 30... Calculator.

Claims (1)

[Claims] 1. An indicator electrode sensitive to ions in a test solution, and a reference electrode provided with a first comparison electrode and a second comparison electrode, the first comparison electrode being immersed in an internal solution. The second comparison electrode has an internal electrode immersed in an internal liquid and a carbon diaphragm interposed between the internal liquid and the test solution. On the other hand, the first
voltage detection means for detecting an electromotive force and a second electromotive force generated between a second comparison electrode and an indicator electrode and having a polarity different from the first electromotive force; A PH and ion concentration measuring device comprising: a reference potential regulator for obtaining a reference potential of an electrode; and a PH and ion concentration measuring device.