Chapter 16 Reference
16.1 pH measurement
218 HORIBA
● Types of pH standard solutions
When measuring pH, the pH meter must be calibrated using a standard solution. There are
several kinds of standard solutions. For normal measurement, three standard solutions
—with a pH of 4, 7, and 9—are sufficient to accurately calibrate the meter.
●
pH 1.68 standard solution: Oxalate
0.05 mol/L tetra-potassium oxalate aqueous solution
●
pH 4.00 standard solution:Phthalate
0.05 mol/L potassium hydrogen phthalate aqueous solution
●
pH 6.86 standard solution: Neutral phosphate
0.025 mol/L potassium dihydrogen phosphate, 0.025 mol/L sodium dihydrogen-
phosphate aqueous solution
●
pH 9.18 standard solution: Borate
0.01 mol/L tetra-sodium boric acid (boric sand) aqueous solution
●
pH 12.45 standard solution: Saturated calcium hydroxide solution
Saturated hydrogenated calcium solution
pH values of pH standard solutions at various temperatures
(NIST(former NBS) settings)
When the standard solutions use U.S. settings, pH 7 is a shown in the below table and pH 9
becomes pH 10.
pH values of pH 7 and pH 10 standard solutions at various temperatures
(US-standard settings)
Calibration is performed using Nernst's equation with the above values.
To Next Page