Instruction Manual
Potassium Electrode
7
A calibration curve is constructed on semi-logarithmic paper when using a
pH/mV meter in the millivolt mode. The measured electrode potential in mV
(linear axis) is plotted against the standard concentration (log axis). In the linear
region of the curve, only three standards are necessary to determine a calibration
curve. In the non-linear region, additional points must be measured. The direct
measurement procedures given are for the linear portion of the curve. The non-
linear portion of the curve requires the use of low level procedures.
6.
To a clean, dry 150 ml beaker, add 100 ml of sample and 2 ml of ISA. Place the beaker on
the magnetic stirrer and begin stirring. Place the electrode tip(s) in the solution. When the
reading has stabilized, record the millivolt reading. Determine the concentration directly
from the calibration curve.
7.
The electrode(s) should be re-calibrated every 1-2 hours. Simply repeat Steps 2-5 above.
Direct Measurement of Potassium (using an ion meter)
1.
By serial dilution of the 0.1M or 1,000 ppm potassium standard, prepare two potassium
standards whose concentration is near the expected sample concentration. Measure out 100
ml of each standard into individual 150 ml beakers and add 2 ml of ISA to each.
2.
Place the more dilute solution on the magnetic stirrer and begin stirring at a constant rate.
Assure that the meter is in the concentration mode.
3.
Lower the electrode tip(s) into the solution.
4.
Adjust the meter to the concentration of the potassium standard and fix the value in the
memory according to the meter manufacturer's instructions after stabilization of the
reading.