3.6 pH Calibration Using Buffers
When performing calibrations two buffer solutions are required, a pH7 and either a pH4 or 10,
dependent on the type of measurement being performed, i.e; acidic (pH4) or alkaline (pH10).
Buffer solutions should be carefully prepared as per the Manufacturers instructions.
Calibration - with Manual Temperature Compensation
1.
Select
°C
on the
Function
switch. Measure the temperature of the buffer solutions. The
instrument display should then be set to the buffer solution temperature measured, using the
Slope/Manual Temp
control.
2.
Select
pH Cal
on the
Function
switch. Immerse the electrode(s) in the pH7 buffer solution.
Allow sufficient time for the pH reading to stabilise. Set the display to the correct value of the
buffer (at the temperature measured in 1.) using the
Buffer
control.
3.
Rinse the electrode(s) in deionised water.
4.
Immerse the electrode(s) in pH 4 or 10 buffer, depending on the type of sample to be tested.
Allow sufficient time for the pH reading to stabilise. Set the display to read the correct value of
the buffer (at the temperature measured in 1.) using the
Slope/Manual Temp
control.
Repeat steps 2-4 until no further adjustments are necessary. Care should be taken when
making adjustments as the controls are interdependent.
5.
Rinse the electrode(s) in deionised water.
6.
Select
pH
on the
Function
switch. When this position is selected the calibration settings are
locked (no further adjustment can be made to the buffer and slope values until the
pH Cal
position is re-selected on the
Function
switch).
7.
If the temperature of the unknown solution differs from the buffer, the Slope/Manual Temp
Control should be used to set the instrument display to the temperature of the unknown
solution.
8.
Immerse the electrode(s) in the unknown solution. The display will indicate the pH value of the
solution.
Calibration - with Automatic Temperature Compensation (ATC)
1.
Select
pH Ca
l on the
Function
switch. Immerse the electrode(s) and ATC probe in the pH7
buffer solution. Allow sufficient time for the pH reading to stabilise. Set the display to read the
temperature compensated value of the buffer solution using the Buffer control.
2.
Rinse the electrode(s) and ATC probe in deionised water.
3.
Immerse the electrode(s) and ATC probe in the second buffer solution. Allow sufficient time
for the pH reading to stabilise. Set the display to read the temperature compensated value of
the buffer solution using the Slope/Manual Temp control.
Repeat until no further adjustments are necessary. Care should be taken when making
adjustments as the controls are interdependent.
4.
Rinse the electrode(s) and ATC probe in deionised water.
350 550/REV A/03-03
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