Performance calibration of pH meters
Although there are many types of PH meters, but their calibration methods are used two-point calibration method, that is, the choice of two standard buffers: the first is the pH7 standard buffer, the second is the pH9 standard buffer or pH4 standard buffer.
Firstly, pH7 standard buffer is used to locate the electrometer, and then the second standard buffer is selected according to the acidity or alkalinity of the solution to be measured. If the solution to be measured is acidic, then choose pH4 standard buffer; if the solution to be measured is alkaline, then choose pH9 standard buffer. If the pH meter is manually adjusted, should be repeated between the two standard buffer several times, until there is no need to adjust its zero and positioning (slope) knob, pH meter can accurately display the two standard buffer pH when it is said that the end of the calibration process. Thereafter, the zero and position knobs should not be moved during the measurement. If the intelligent pH meter, there is no need for repeated adjustments, because its internal storage of several standard buffer pH can be selected, and can be automatically identified and automatically calibrated. But pay attention to the choice of standard buffer and the accuracy of its preparation. Intelligent 0.01 level pH meter generally have 3 kinds of memory ~ 5 kinds of standard buffer.
Secondly, special attention should be paid to the temperature of the solution to be measured before calibration. In order to correctly select the standard buffer, and adjust the temperature compensation knob on the panel of the meter, so that it is consistent with the temperature of the solution to be measured. Different temperatures, the standard buffer solution pH is not the same (see Table 2-3).
After the calibration work, the frequent use of the pH meter in general within 48h do not need to calibrate again. If you encounter one of the following situations, you need to recalibrate.
(1) the solution temperature and the calibration temperature has a large difference.
(2) The electrode is exposed in the air for too long, such as more than 30min.
(3) Positioning or slope regulator has been activated by mistake.
(4) After measuring a solution that is too acidic (pH<2) or too alkaline (ph>12).
(5) After changing the electrodes
(6) When the pH of the measured solution is not in the middle of the solution selected for the two-point calibration and is far away from pH 7.
