VWR 662-2380, Instruction Manual

Page: 26 / 52

- 22 -
11. CHECKING THE ELECTRODE CONDITION
After pH electrode calibration the meter calculates its parameters: offset in pH
units and slope defined also as efficiency in precents.
The electrode offset may be defined in pH or mV units.
An ideal electrode immersed in the 7.00 pH buffer before calibration should
indicate 7.00 pH which equals 0.00 mV. If the reading is different, it informs
that the electrode has an offset, which may be reduced by calibration. The
information about the offset in mV may be obtained by converting the reading
in pH. At 20 °C each pH unit corresponds to 58.168 mV. If the electrode has
0.2 pH offset, multiply it by 58.168 mV to obtain the electrode potential value
in mV (SEM – Standard Error of Measurement). In the given example it will
be equal 11.634 mV.
The SEM parameter may be also checked by immersing the electrode in 7.00
pH buffer and switching the meter to measurement in mV.
When the electrode is calibrated, its condition may be checked. To check,
enter the calibration points screen according to description in the point 9.4.
The top left of the screen (Pic. 4C) displays the electrode number and below
the calibration date two parameters, determined during the last calibration are
displayed:

(zero offset in pH) and

(condition in %).
Yellow colour of the electrode number signalises:
- electrode condition loss, if the zero and condition parameter are
displayed in yellow;
- calibration validity date expiry if the last calibration date is also displayed
in yellow.
In case of 1 point calibration, only the zero offset parameter is displayed.
User‘s manual for PH-2500L pH meter v1.0x