pH/mV Temperature Meter
430-020
9 9907X0088 Issue 2
‘
FAIL
’ will be shown if 7.00 pH buffer isn’t used as the first calibration point.
If the electrode and buffer solution’s combined error is greater than 0.5 pH or
30mV then ‘
Error I/P
’ will be displayed and the calibration aborted. If the
electrode and buffer solution’s combined error is greater than 30mV then
‘
FAIL
’ will be displayed and the calibration aborted. If the electrode and
buffer solution’s combined slope error (4.01 or 10.01) is greater than 0.5pH
or 15% ‘
Slope error
’ will be displayed. If the slope error is greater than 15%
the ‘
FAIL
’ will be displayed.
If an error is displayed during a correctly performed pH calibration this can
be investigated using the mV reading from the pH electrode to determine if
the electrode needs to be replaced. With the instrument in mV mode place
the clean/conditioned electrode and temperature probe into buffer pH 7.00 at
a temperature of 25°C and leave for 30 seconds to stabilise. Record the mV
reading (Asymmetry Potential). Rinse the electrode and temperature probe
in distilled or deionised water, blot and repeat the process in buffer pH 4.01.
Record the mV reading and calculate the difference between the two to
obtain the span.
Example:
Reading at 7.00 pH: 4 mV
Reading at 4.01 pH: 178 mV
Span = 178
– 4 = 174mV
In order to calculate the slope percentage (Condition), divide the calculated
span by the theoretical span and times it by 100. The theoretical span
between 7.00 pH and 4.01 pH is 176.9 mV.
Slope % = 174/176.9 x 100 = 98%
If your results are below 85% or your mV reading exceeds ±30mV at 7pH,
then you will need to replace the electrode.
Once the instrument is calibrated the sample can be measured. Place the
pH electrode and temperature probe into the sample and allow to stabilise.
