Technical Buffers
Use first buffer
Continue...
CALIBRATING pH
Technical Buffers
Use second buffer
Continue...
CALIBRATING pH
Technical Buffers
Use third buffer
Continue...
CALIBRATING pH
...
Start calibration
Channel 1
Technical buffers
1st buffer OK
pH 7.01 23˚C
00:30
CALIBRATING
1st buffer
pH
7.15 25˚C
00:23
CALIBRATING
1st buffer
pH
7.15 25˚C
Stirring
23%
00:23
CALIBRATING
2nd buffer
pH
4.12 23˚C
00:20
2nd buffer OK
pH 4.01 23˚C
00:26
Channel 1
pH CALIBRATION
10-04-2010 17:15
CALIBRATING
1st buffer
pH 7.15
25˚C
00:23
4. Operation
4.5. pH calibration
To measure pH correctly, the electrode and the instrument set
need to be calibrated regularly with buffer solutions . This
compensates deviations of asymmetry potential and slope of the
electrode over time .
The calibration with buffer solutions corrects variations in the
electrode response .
The instrument allows one-, two- and three- point calibration .
The calibration parameters remain in memory until a new calibra-
tion is performed .
The standard calibration is performed with technical buffers and
standard stability criterion . In addition, the instrument offers
other options for calibration .
It is highly recommended to apply the same stability criteria to
measure and calibrate .
One-point calibration
This type of calibration is acceptable when measuring pH values
similar to those of the buffer solution .
It corrects the asymmetry potential of the electrode .
Two-point calibration
This is the most common calibration .
It is recommended to start with pH 7 as first buffer . pH 4 or pH 9
buffers can be used as a second buffer, depending on the meas-
ured zone (acid or alkaline) .
The two-point calibration compensates the asymmetry potential
and the electrode’s sensitivity (slope) .
Three-point calibration
This type of calibration is recommended when measurements are
made across the whole pH scale .
As a first point pH 7 is recommended .
For the second and third points, two of the remaining values
must be chosen .
The three-point calibration pH 4 .00, 7 .01 and 9 .21 (at 25ºC,
77ºF) compensates the asymmetry potential and electrode’s
sensitivity in the acid and alkaline zone .
Calibration with technical buffers
Buffers pH 4 .00, 7 .01 and 9 .21 (at 25ºC, 77ºC) are supplied
together with the instrument .
Preparation
Fill the flasks with the corresponding buffer solution (40 ml) .
These buffers can be used to perform more than 10 calibrations .
Every calibration flask is supplied with a magnetic bar .
Diagram for calibration
8
Important note:
The pH value of the buffer appearing on the display depends on
the temperature of calibration . See buffers pH values as a func-
tion of the temperature on page 19 .
To modify the
standard calibra-
tion see page 9.
The instrument
controls automati-
cally the start/stop
of the stirrer.
Modify temperature
Modify stirring
