User manual

9 This text disappears when the reading is stable and the
following text is then shown:
10 Adjust the pH value in the display using the dial so that it
corresponds to the known pH value of the second buffer
solution and press OK.
11 When the two point calibration is performed successfully,
the following text is shown for one second:
12 From the
Calibrate pH Buffer 2 menu, turn the dial one step
clockwise to access sub menu Calibrated Electrode Slope.
This menu shows the slope of the calibration curve,
where 100% corresponds
to 59.16 mV per pH step
at 25 °C. The asymmetry
potential at pH 7 is
shown as a mV value.
Press ESC to return to
the Set Parameters menu.
13 Before use, rinse the
electrode using distilled
water.
A new electrode typically has a slope of 95 - 102% and an
asymmetry potential within ±30 mV. As the electrode ages, the slope
decreases and the asymmetry potential increases.
As a rule, when an electrode has an asymmetry potential outside of
±60 mV and a slope lower than 80%, and no improvement can be
achieved by cleaning, it should be replaced.
An electrode is still usable at lower slopes and higher asymmetry
potentials but the response will be slower and the accuracy
diminished.
Calibrating with the electrode in the flow cell
When calibrating with the electrode fitted in the flow cell in
ÄKTA
FPLC, follow the above procedure but let at least 30–35 ml
(with 2 ml mixer) of standard buffer solution be pumped through
the system to stabilize pH. Leave the pump running while
calibrating. Switch to the second standard buffer solution and repeat
the procedure. For a description of calibration from UNICORN with
the electrode fitted in the flow cell, see Chapter 6 in the UNICORN
User Manual.
Voltage (mV)
pH
0 mV
+500 mV
–500 mV
7
Asymmetry
potential
at pH 7
Calibration curve
Calibrated Electrode
Calibration OK
Calibr pH Buffer 2
Calibr pH Buffer 2
Monitor UPC-900
User Manual 18-1125-55 Edition AE
18
3 Operation
The calibration curve
shows the relationship
between pH and the
output signal from the
monitor in mV.