JP2524740B2 - Calibration method of PH meter - Google Patents

Description

The present invention relates to a method for calibrating a pH meter.

[Conventional technology]

When calibrating the electrodes of a pH meter, there are five standard buffer solutions whose adjustment method is specified by JIS standards, and the standard solutions whose pH at 25 ° C are 1.68, 4.01, 6.86, 9.18, 10.02, respectively. Used as a calibration solution.

The five standard buffer solutions are oxalate standard solutions [0.
05M tetrapotassium oxalate _{KH 3 (C 2 O 4)} 2 · 2H 2 O aqueous solution],
Phthalate standard solution (0.05 M potassium hydrogen phthalate C ₆ H ₄ (C
OOK) (COOH) aqueous solution], neutral phosphate standard solution [0.025M
Monopotassium phosphate KH ₂ PO ₄ −0.025M Disodium phosphate Na
₂ HPO ₄ aqueous solution], borate standard solution [0.01 M sodium borate (borax) Na ₂ B ₄ O ₇ · ₁₀ H ₂ O aqueous solution], carbonate standard solution [0.025 M sodium hydrogen carbonate NaHCO ₃ -0.025 M carbonate Sodium Na ₂ CO ₃ aqueous solution].

And to adjust the standard buffer solution, the conductivity should be 2 × 10 ^-6.
Pure water of Ω ^-1 cm ^-1 (at 25 ° C) or less is used.
The oxalate standard solution is potassium tetraoxalate (JIS K847
(4, pH measurement) 12.71 g is dissolved in the above pure water to make 11 solution.

FIG. 4 shows the procedure of the conventional calibration method. In the figure, “preservation” means that the adjusted standard solution is sealed and stored in a bottle made of high quality glass or polyethylene. A calibration solution containing the standard solution thus adjusted and stored is commercially available as an accessory for the pH meter.

[Problems to be solved by the invention]

By the way, since the pH meter can perform the most accurate measurement during calibration, it is necessary to calibrate it as necessary when measuring pH, and the above calibration solution is indispensable for pH measurement. Regardless of the time, in the case of outdoor measurement or measurement in the field work, it is necessary to carry the calibration solution and cleaning water set as above together with the pH meter, which has the drawback of being very bulky, and also in outdoor measurement etc. Was extremely difficult to calibrate, and it was difficult to calibrate accurately, which was an obstacle to accurate pH measurement.

The present invention has been made in consideration of the above matters, and its purpose is to use a calibration sheet that is easy to carry and easy to handle, and a pH that can be easily calibrated during measurement. It is to provide a calibration method for the meter.

[Means for solving problems]

In order to achieve the above-mentioned object, the calibration method of the pH meter according to the present invention, the calibration buffer solution is absorbed into a water-absorbent sheet having chemically stable water absorption without ion elution, and then dried. The calibration sheet is characterized in that it is brought into contact with a pH electrode having a planar structure and a prescribed amount of pure water is dropped on the calibration sheet to perform a prescribed calibration.

[Action]

The calibration method of the pH meter according to the present invention is such that after absorbing the calibration buffer solution in the water absorbing sheet, the dried calibration sheet is placed on the pH electrode having a planar structure and pure water is dropped on the calibration sheet. Calibration can be performed with just a simple operation.

Furthermore, in the present invention, the calibration buffer solution is absorbed in the calibration sheet. Therefore, the pH value is constant even if the amount of the pure water dropped on the calibration sheet changes to some extent, and therefore, when the pure water is dropped on the calibration sheet, the drop amount of the pure water is strictly adjusted. It does not have to be lightweight.
In short, by using the calibration buffer solution, it is possible to allow the fluctuation of the amount of the pure water to be dropped, and to easily perform the dropping operation.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows each step from the production of the calibration sheet for the pH meter according to the present invention to the calibration of the pH meter using this calibration sheet. For example, a calibration sheet for pH 4 and pH 7 is taken as an example. explain.

First, weigh 10.21 g of potassium hydrogen phthalate (JIS K8809, for pH measurement) and add phosphate-potassium (JI
3.40 g of S K9007, for pH measurement) disodium phosphate (JI
Weigh 3.55 g of S K9020 (for pH measurement) (see S1).

Then, 10.21 g of the above potassium hydrogen phthalate was dissolved in pure water having an electric conductivity of 2 × 10 ⁻⁶ Ω ⁻¹ cm ⁻¹ (at 25 ° C.) or less (hereinafter referred to as pure water for adjustment) to obtain 11 phthalic acid. Make a salt standard solution. On the other hand, 3.40 g of potassium-potassium phosphate and 3.55 of disodium phosphate are dissolved in pure water for adjustment to prepare 11 neutral phosphate standard solutions (see S2).

Then, the phthalate standard solution and the neutral phosphate standard solution are weighed and put in separate containers in predetermined amounts (S3
reference).

Next, the absorbent sheet is immersed in the standard solution in each of the above-mentioned containers so that the absorbent sheet absorbs the solution (see S4).

Here, the material of the absorbent sheet is preferably one that is chemically stable without ion elution and rich in water absorption,
For example, in addition to the above-mentioned properties, in addition to a polymer material having high flexibility and good adhesion to an electrode, an inorganic material such as glass or ceramic fiber may be used.

In this example, a non-woven fabric made of 100% cellulose (having a thickness of about 220
μm) was used as an absorbent sheet.

Then, the absorbent sheet that has absorbed the standard solution as described above is dried at room temperature, and the calibration sheets for pH 4 and pH 7 are used.
Is obtained (see S5 and FIG. 2).

In this case, after evaporation of water, it is important to dry the powder of the dried component fine particles so as not to be separated from the absorbent sheet.

The calibration sheets 1 and 2 obtained as described above are appropriately packaged and stored (see S6). It should be noted that these calibration sheets 1 and 2 are set together with other calibration sheets that have absorbed other standard solutions, and are commercially available as accessories for the pH meter.

And to calibrate the electrode of the pH meter when measuring pH,
As shown in FIG. 3, for example, Japanese Patent Application No.
-285371, the calibration sheet 1 (2) is placed in close contact with the surface of the pH electrode 3 having a planar structure, and the pure water for adjustment shown in S2 in FIG. Pure water 4 in an amount substantially equivalent to the pure water for adjustment used when the standard solution was prepared by addition is dropped. By dropping this pure water 4, the standard solution before drying is again obtained in the calibration sheet 1 (2), and the pH electrode is calibrated by this standard solution.

As described above, in the present embodiment, the calibration sheets 1 and 2 can be calibrated by a simple operation of placing the calibration electrodes 1 and 2 on the planar pH electrode 3 and dropping pure water 4 onto the calibration sheets 1 and 2. In addition, since the calibration buffer solution is used, even if the amount of the pure water dropped on the calibration sheet changes to some extent, the pH
Since the value is constant, it is not necessary to strictly measure the dropping amount of the pure water when dropping the pure water on the calibration sheet, and the dropping operation can be easily performed.

The pH electrode 3 having the above-mentioned planar structure was calibrated by using the calibration sheet obtained by absorbing the standard solution with the absorbent sheet made of the non-woven fabric of 100% cellulose used in this example, and reproduced. And the reproducibility test after standing for several days were both good.

Of the pH standard buffer solutions, the borate standard solution and carbonate standard solution may absorb carbon dioxide gas and cause the pH to drop significantly, so absorb these standard solutions in an absorption sheet for calibration. When a sheet is obtained, it is preferable to carry out the treatment in an inert gas atmosphere from the step of absorbing the standard liquid in the absorbent sheet so that the sheet is not exposed to the atmosphere during drying and storage.

〔The invention's effect〕

As described above, the calibration method of the pH meter according to the present invention, after absorbing the calibration buffer solution in the water-absorbing sheet, the dried calibration sheet is placed on the pH electrode having a planar structure to obtain pure water. Calibration can be performed by a simple operation of simply dropping it on the calibration sheet.

Furthermore, in the present invention, the calibration buffer solution is absorbed in the calibration sheet. Therefore, the pH value is constant even if the amount of the pure water dropped on the calibration sheet changes to some extent, and therefore, when the pure water is dropped on the calibration sheet, the drop amount of the pure water is strictly adjusted. You do not need to weigh.
In short, by using the calibration buffer solution, it is possible to allow the fluctuation of the amount of the pure water to be dropped, and to easily perform the dropping operation.

[Brief description of drawings]

1 to 3 show one embodiment of the present invention, and FIG. 1 shows each step from the production of the calibration sheet of the pH meter according to the present invention to the calibration of the pH meter using this calibration sheet. FIG. 2, FIG. 2 is a perspective view showing an example of the above calibration sheet, and FIG. 3 is a diagram for explaining the calibration method. FIG. 4 is a chart for explaining the conventional technique. 1,2 ... Calibration sheet, 3 ... Planar pH electrode, 4 ...
…Pure water.

Claims (1)

(57) [Claims] 1. After absorbing a calibration buffer solution into a water-absorbing sheet having a chemically stable water-absorbing property without ion elution,
The dried calibration sheet is brought into contact with a pH electrode having a planar structure, and a predetermined amount of pure water is dropped onto the calibration sheet to perform a predetermined calibration.
Calibration method of pH meter.