VWR 662-2380, Instruction Manual

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10. CALIBRATION
Before starting measurement with a new electrode or before making
measurements which require high accuracy, the electrode connected to the
meter should be calibrated. Results of measurements made without
calibration will be burdened with a significant error. Calibration is performed in
the buffer or standard solutions. It consists in comparing pH value of the
standard solutions with the reading displayed by the meter and automatic
correction which is taken into consideration during the next measurements.
Calibration should be periodically repeated because the parameters of the
electrode in use are changing, what influences the accuracy. The frequency
of this procedure depends on the required accuracy, number of the
measurements carried out, conditions in which the electrode was used,
temperature and value of the measured solutions.
PH-2500L enables storing characteristics of three calibrated pH electrodes
separately, recorded under different numbers ( E1 , E2 or E3 ). This feature is
very useful when it is necessary to change the electrode quickly or to replace
a broken one.
The meter enables entering the calibration validity expiry date for each of the
electrodes separately. If this option is active, the calibration should be
performed when the applied electrode number (
E1 , E2 or E3 ) turns yellow.
For obtaining optimal calibration results, the pH values of the applied
solutions should be entered to the meter’s memory by the user. During
calibration, after putting the pH electrode and the temperature probe into
solution, the meter detects its pH value automatically. When the highest
accuracy is required, it is recommended to use certified standard solutions.
However, the most often used are buffer solutions of total values i.e. 2.00 pH,
4.00 pH etc, with a composition specified by the manufacturer. They are also
of quite high accuracy.
For accurate measurements it is necessary to use fresh solutions of good
quality.
The temperature changes have a great influence on the pH value of
standards and buffer solutions. The manufacturers usually specify the pH
values of a solution in a specific temperature. During accurate calibration the
stored solution value has to be the same as the value of this solution in the
temperature in which the calibration is performed. If the electrode number
turns yellow after the calibration is finished, it informs that the electrode lost
its efficiency and will have to be replaced soon. An additional information is
shown on the electrode calibration points screen (description in the
chapter 11).
User‘s manual for PH-2500L pH meter v1.0x