JPH03128452A - Method for discriminating ph standard liquid - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for determining a pH standard solution (hereinafter simply referred to as a standard solution as necessary), and more specifically, the present invention relates to a method for determining a pH standard solution (hereinafter simply referred to as a standard solution as necessary). The present invention relates to a method for determining pH standard solutions that enables automatic determination of the types of two preselected standard solutions.

(Prior Art) Conventionally, this type of automatic discrimination method for standard solutions has been disclosed, for example, in Japanese Patent Publication No. 13147/1983 and German Patent No. 2937227.
Those shown in the number are known. These automatic discrimination methods are based on the fact that, for example, the electromotive force generated when a pH measurement electrode is immersed in three common types of B'$ solutions among the standard solutions specified by JIS can be calculated in advance. The range of electromotive force (potential) for each standard solution in the practical temperature range is set appropriately, and in which potential range the electromotive force falls when the electrode is immersed in the standard solution to be discriminated. The purpose is to determine the type of standard solution depending on which type it belongs to.

However, in these methods, the potential range is set in consideration of the maximum value and minimum value of the electromotive force, the 811 constant error of each electrode, etc., but this potential range is set regardless of the temperature. However, when the electrode deteriorated, a misjudgment of the standard solution may occur. In view of this point, another conventional automatic discrimination method is disclosed in Japanese Patent Application Laid-Open No. 63-269048. This discrimination method calculates the pH value when the electrode is immersed in the standard solution at a certain measurement temperature, and then refers to the pH value-temperature characteristic table of each standard solution stored in advance in the memory to determine the pH value that best matches the above-mentioned pH calculation value. This method selects the pH values that are close to each other and determines the type of standard solution.

According to this automatic discrimination method, the temperature-compensated pH calculation value according to the measured temperature at that time is compared with the pH value of the standard solution at that temperature. It is now possible to distinguish.

(Problems to be Solved by the Invention) However, in the automatic discrimination method disclosed in Japanese Patent Publication No. 63-13147, etc., as shown in FIG.

For example, the potential range V, , V1 corresponding to pH 9 and pH 10
0 is the potential range V2mV of other pH2, pH4, pH7, etc.
4. Since it is inherently narrow compared to V, if the electromotive force measured for a certain standard solution can take a value within the range like Vx in the figure due to changes in the characteristics of the electrode used at that time,
In some cases, it was not possible to determine whether the type of standard solution was a pH 9 standard solution or a pH 10 standard solution.

More specifically, the asymmetric potential of a glass electrode allowed by JIS is ±30 mV, which theoretically corresponds to about ±0.5 pH. Therefore, taking into account variations in electrode characteristics, deterioration, etc., accurate determination cannot be made unless the pH values of the standard solutions differ by at least 1 or more.

When the measurement temperature is 25°C, the pH values of the standard solutions of pH 9 and pH 10 are 9.18 and 10.01, respectively, and the difference between the two is 0.83 (the theoretical value is 49 when converted to fil pressure).
．． 1 mV), it is difficult to distinguish between the pH 9 and pH 10 standard solutions using any of the conventional methods described above.

The present invention has been made to solve the above problems,
The purpose of this is to reliably identify the type of standard solution even if there are variations or deterioration in the characteristics between the electrodes. It is an object of the present invention to provide a method for determining pH standard solutions that also enables determination of pH standards.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for determining a pH standard solution used for standard solution calibration of a pH measuring device.
Two preselected standard solutions whose individual types are unknown (for example, one is a standard solution with pH 4 and the other is pH 7)
(or two types of standard solutions, one of which is clearly a pH 9 standard solution and the other a pH 10 standard solution, but the type cannot be identified individually) using a pH measuring device. For f! The type of each of the two types of pH standard solutions is determined based on the magnitude of the electromotive force when the i-electrode is sequentially immersed.

(Function) According to the present invention, each standard is determined based on the magnitude of electromotive force when a pH measurement electrode is sequentially immersed in two types of standard solutions whose types are clearly known as a whole even if the individual types cannot be identified. The type of liquid can be identified and discriminated.

After determining the type of standard solution, perform standard solution calibration using the pH value at the measurement temperature by referring to the pH value-temperature characteristic table of the standard solution prepared in advance for each standard solution. be able to.

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

Figure 1 shows the configuration of this embodiment.
Reference numeral 1 designates a pH measuring electrode incorporating a glass electrode and a reference electrode, and 2 a temperature detection element, to which input sides of amplifiers 3 and 4 are connected.

The output terminal of the amplifier 3.4 is connected to a changeover switch 5, which is configured to be able to constantly input electromotive force and temperature by switching the switch 5 at short intervals in response to commands from a CPU 7, which will be described later.

On the output side of the changeover switch 5, an A/D converter 6 and a CPU are connected.
7 and a display 8 are connected in sequence. Here, A/D
The converter 6 converts the analog output signal of the amplifier 3 or 4 selected by the changeover switch 5 into a digital signal,
Further, the CPU 7 executes a predetermined program for measurement, calibration 1 display, etc., and also controls the operation of the changeover switch 5, and the display 8 is for digitally displaying the measured pH value, etc.

On the other hand, the CPU 7 is connected to a measurement/calibration changeover switch 9 for switching between measurement mode and calibration mode, a ROM II that stores programs for measurement and calibration, and a RAM 12 that stores measurement data. There is. Note that ROMII has pH 2, pH 4, pH 7, p
A pH value-temperature characteristic table showing the pH value at the measurement temperature is stored for each standard solution such as H9 and pH10.

Furthermore, in this embodiment, a standard solution selection switch 10 such as a dip switch for selecting the type of standard solution used during calibration is connected to the CPU 7. This switch 1
0 means that the type of each standard solution cannot be specified, but for example, it is clear that one of them is a standard solution with a pH of 9 specified by JIS and the other is a standard solution with a pH of 10. When performing calibration using , the type of standard solution mentioned above (pH 9, pH 10) is selected by turning on the switch and manually inputted to the CPU 7. In addition to the dip switch, the numeric keypad switch on the keyboard etc. is used. You can.

Here, by using the standard solution selection switch 10, for example, pH 9,
Selecting pH1o means that the pH value-temperature characteristic table in ROMII corresponding to these standard solutions is selected by the CPU 7, and the standard solution calibration described below is performed based on the contents of this table. .

Although not shown, a data import switch is connected to the CPU 7 for determining the timing of data import during calibration.

Next, the automatic discrimination function of the standard solution in this embodiment will be explained.

First, switch the measurement/calibration selector switch 9 to calibration mode, prepare two types of standard solutions, for example, pH9 and pHIO (assuming that it is unclear which one is pH9 (or pH1o)), and press the standard solution selection switch IO. pH9,
Turn on the switch corresponding to pH 10.

Next, with the changeover switch 6 connected to the amplifier 3 side, one of the standard solutions 100□ as the test solution 100 shown in FIG.
The pH measuring electrode 1 is immersed in the liquid to measure the electromotive force V■, and this value is held in the RAM 12. Then, when the changeover switch 5 is switched to the amplifier 4 side, the 4111 semi-liquid 10
The temperature of 01 is measured by the temperature detection element 2 and
hold within.

Next, for the other standard solution 100□, measure the electromotive force V■ in the same manner as above, measure the temperature, and calculate these values as R.
Retained in AM12.

Here, as shown in FIG. 2, there is a linear relationship between the pH value and the electromotive force V. For example, the electromotive force V corresponding to a standard solution with a pH of 9
The relationship Va > V b holds between a and the electromotive force vb corresponding to the pHIO standard solution, and this relationship does not change even if there are changes in the characteristics of the electrode or temperature, so there are two types. Electromotive force V measured for the standard solution of
By comparing the magnitude relationship between and V■ in the CPU 7, it becomes possible to automatically determine which standard solution is the one with pH 9 (or pI (10)).

After determining the type of each standard solution in this way, the CPU
In step 7, the pH value-temperature characteristic table for each standard solution of pH9 and pHIO can be referred to by operating the standard solution selection switch
The pH value corresponding to the measurement temperature can be determined for each of the 10 standard solutions.

By performing standard solution calibration using the two types of standard solutions whose pH values have been determined in this way, it is possible to measure the test solution 100 whose pH value is unknown. The electromotive force may be measured using the pH measurement electrode 1 with the pH measurement electrode 9 set in the measurement mode.

Note that if the combination of two types of standard solutions discriminated by the present invention is unchanged and it is planned to always perform calibration using these standard solutions, the standard solution selection switch 1o in the above embodiment is omitted and only the pH value-temperature characteristic table for the two types of standard solutions is used in ROMII.
You can prepare it in your home and perform JB quasi-liquid calibration.

In addition, in the above embodiment, in comparison with the conventional technology, the discrimination between standard solutions of pH 9 and pH 10, which are used relatively infrequently, was explained, but the present invention
This method can be applied to distinguish between any two types of standard solutions, such as the standard solution No. 7.

Furthermore, pHI! The I constant electrode is not limited to a glass electrode, but may also be an Achmon electrode, an FET sensor, or the like.

Furthermore, the principle of the present invention of determining the type of standard solution based on the magnitude relationship of electromotive force can of course be applied to determining three or more types of standard solutions in multi-point calibration.

(Effects of the Invention) As described above, according to the present invention, the electromotive force is sequentially measured for two preselected standard solutions whose individual types cannot be identified, and the types of the two standard solutions are determined based on the magnitude relationship. i! for pH measurement. Even if there are individual differences in the characteristics of the electrodes, deterioration of the electrodes, temperature changes within the normal range, etc., the type of standard solution can always be accurately determined.

In particular, even when the difference in electromotive force is inherently small, such as between pH 9 and pH 10, the magnitude relationship of electromotive force for each pH value for the same electrode is usually determined in a similar way, so accurate automatic discrimination of standard solutions is difficult. This makes it possible to prevent calibration errors caused by mixing up standard solutions and contribute to smoother and faster work.

Furthermore, in the present invention, the type of standard solution can be determined by simply comparing the magnitude relationship of electromotive force, so the program on the CPU can be simple, and there is no risk of increasing the load on the CPU. has.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing one embodiment of the present invention, Figure 2 is a pH
FIG. 3 is a diagram showing the relationship between pH value and electromotive force, and is an explanatory diagram of potential ranges corresponding to each pH value, for explaining the conventional technology. 1... Electrode for pH measurement 2... Temperature detection element 3.
4...Amplifier 5...Mode selection switch 6.
...A/D converter 7...CPU8...Display unit 9...Measurement/calibration changeover switch 10...Standard solution selection switch

Claims (1)

[Claims] In a method for determining a pH standard solution used for standard solution calibration of a pH measuring device, when the pH measuring electrode of the pH measuring device is sequentially immersed in two types of pre-selected pH standard solutions. A method for determining a pH standard solution, comprising determining the type of each of the two types of pH standard solutions based on the magnitude of the electromotive force.