Horiba Scientific 6561S-10C, Instruction Manual

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67
Reference

Impact of pH
The usable pH range is determined depending on the type and the
structure of the ion selective electrode.
In general, this range is smaller when the concentration of the ions to be
measured is lower.
Also, depending on the ion selective electrodes, the components of the ion
selective membrane may be dissolved by the pH or the electrode potential
may change due to the impact of the pH.
Furthermore, the impact of the pH may cause a decrease in the slope of
the ion selective electrode, or parallel shifting of the calibration curve.
To prevent these effects, set the pH to an appropriate value in advance and
keep it constant.
One simple method to set the pH of the sample solution to an appropriate
value for measurement is to prepare a pH buffer solution (not containing
interfering ions) that will not interfere with the ion selective electrode in
advance, and add a small amount of it to the sample solution.
Impact of pH on fluoride ion selective electrode is shown in Fig. 9.
Fig. 9 Impact of pH on fluoride ion selective electrode
0
6 7 8 9 10 11 12
50
100
150
Electromotive force (mV)
pH
Impact of pH
0.1 mg/L
1 mg/L
10 mg/L