NAVI D-25, Instruction Manual

Page: 187 / 227

7 Reference
7.1 pH measurement
176 HORIBA
●
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 forces
caused by temperature. There is absolutely no relation
between the change in pH caused by the temperature of
the solution and temperature compensation. This is
often misunderstood. When pH is to be measured, the
temperature of the solution when the pH is measured
must be recorded along with that pH value, even if a
meter that has automatic temperature compensation is
used. If the solution temperature is not recorded, the
results of the pH measurement are relatively
meaningless.
●
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 dihydrogenphosphate 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