6 Reference
103
6.3
pH measurement
6.3.1
Principle of pH measurement
U-50 series use the glass electrode method for pH measurements. The glass electrode
method measures a potential difference between the glass film for pH and the reference
electrode. For more information, refer to “JIS Z 8802 pH measurement method”.
6.3.2
Temperature compensation
The electromotive force generated by the glass electrode changes depending on the
temperature of the solution.
Temperature compensation is used to compensate for the change in electromotive force
caused by temperature.
This function does not compensate the change in pH caused by the temperature of the
solution. When pH is to be measured, the temperature of the solution must be recorded along
with that pH value, even if a pH meter has automatic temperature compensation function. If
the solution temperature is not recorded, the results of the pH measurement may be
meaningless.
6.3.3
Standard solutions
When measuring pH, the pH meter must be calibrated using standard solution. There are five
kinds of standard solutions specified in “JIS Z 8802 pH measurement”. For normal
measurement, two of standard solutions with pH of 4, 7, and 9 are sufficient to accurately
calibrate the meter.
For standard solutions, refer to “JIS Z 8802 pH measurement”.
Table 4 pH values of HORIBA pH standard solutions at various temperatures settings
pH 4 standard solution:
(Phthalate)
0.05 mol/L potassium hydrogen phthalate aqueous solution
pH 6.86 standard solution:
(Neutral phosphate)
0.025 mol/L potassium dihydrogenphosphate, 0.025 mol/L
disodium hydrogenphosphate aqueous solution
pH 9 standard solution:
(Borate)
0.01 mol/L sodium tetraborate aqueous solution
Temp.
(
℃
)
pH 4 standard solution
Phthalate
pH 6.86 standard
solution
Neutral phosphate
pH 9 standard solution
Borate
0 4.01 6.98 9.46
5 4.01 6.95 9.39
10 4.00
6.92
9.33
15 4.00
6.90
9.27
20 4.00
6.88
9.22
25 4.01
6.86
9.18
30 4.01
6.85
9.14
35 4.02
6.84
9.10
40 4.03
6.84
9.07
45 4.04
6.84
9.04
Summary of Contents for U-51
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