Section 2 -
pH Calibration and Measurement
For accurate results, stir all buffers and samples. Always rinse electrodes and blot dry
before transferring from one solution to another to prevent contamination. Ensure that any
electrode filling holes are left uncovered during use.
Automatic Temperature Compensation
1.
Connect the pH electrode(s) and temperature probe and turn the mode switch to °C
2.
Place the pH electrode(s) and the temperature probe in the first buffer, and note the
temperature of the solution. Refer to the temperature chart on the buffer (or see
Appendix 1) and note the correct value of the buffer at the noted temperature.
3.
Turn the mode switch to pH mode. Wait for the reading to stabilise. Using the CAL
control, adjust the reading to the value obtained in step 2.
4.
Place the pH electrode(s) and temperature probe in the second buffer. Again establish
the correct value for the temperature of measurement. When the reading is stable,
adjust to the correct value using the Slope control.
5.
Automatically temperature compensated readings may now be made by immersing the
pH electrode(s) and temperature probe into the sample and recording the stabilised
reading.
Manual Temperature Compensation
If use of a temperature probe is inappropriate (e.g. small sample size), then it is possible to
use manual temperature compensation).
1.
Disconnect temperature probe.
2.
Measure the temperature of the buffer with a thermometer.
3.
Switch to °C mode and adjust the reading to the correct value using the Temp °C control.
4.
Refer to the temperature chart on the buffer (or see Appendix 1) to establish the correct
buffer value for the temperature of measurement.
5.
Follow the procedure given above for Automatic Temperature Compensation, points 3.
to 5. above, measuring and adjusting the temperature manually for each buffer and
sample.
No Temperature Compensation
For accurate results with no temperature compensation, the temperature of all buffers and
samples should be equal and remain constant.
1.
With the temperature probe disconnected, switch the instrument to °C mode and set the
displayed reading to the temperature of measurement using the Temp °C control.
2.
Switch to pH mode, place the electrode(s)in the first buffer, wait for the reading to
stabilise and enter the correct value (given on the buffer packet or in Appendix 1) using the
CAL control.
3.
Place the electrode(s) in the second buffer. When the reading is stable, adjust to the
correct value using the Slope control.
4.
Place the electrode(s) in the sample and record the stabilised reading.
