horiba 5002S-10C, Instruction Manual

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58

Impact of pH
The ammonia electrode can be used in the specified pH range. The impact
of the pH may cause a decrease in the slope of the ammonia electrode, or
parallel shifting of the calibration curve.
To prevent these effects, add an appropriate amount of pH-adjusting ISA to
keep the pH of the solution constant in advance.

Impact of temperature
The potential gradient measured by the ion electrode method
*
is impacted
by the temperature of the sample solution in accordance with the Nernst
equation
**
. The higher the temperature is, the larger the potential gradient
is. The lower the temperature is, the smaller the potential gradient is.
The standard solution in calibration and the sample solution in
measurement shall have almost the same temperature. Match the
temperature as close as possible.
Table 3 Relationship between temperature of ion
selective electrode and theoretical slope

：
This is the method to measure the ion concentration by measur-
ing potential difference between ion selective electrode and ref-
erence electrode soaked in the sample solution.

：
This is the equation which shows the logarithmic proportional
relationship between the potential gradient and the ion concen-
tration (activity) in a sample solution.
Unit: mV/decade (mV/concentration change of 10 times)
Temperature (°C)
0 10 20 25 30 40 50
Theoretical
slope
Monovalent
ions
54.20 56.18 58.16 59.16 60.15 62.13 64.11
Divalent
ions
27.10 28.09 29.08 29.58 30.07 31.07 32.06