Any pH meter must be calibrated pH standard solution only after the measurement of pH value of the sample, the sample measurement accuracy under 0.1pH, using a point calibration method of adjusting instrument, generally used in the pH6.86 or pH7.00 standard buffer solution. Some instruments are only 0.2pH or 0.1pH in accuracy, so the instrument only has a "positioning" adjustment knob. The specific steps are as follows:
(1) measure the temperature of the standard buffer, check the table to determine the pHs value at this temperature, adjust the temperature compensation knob to this temperature.
(2) rinse the electrode with pure water and dry it.
(3) the electrode is placed in the buffer solution and then placed stationary. When the reading is stable, the positioning knob is adjusted to make the instrument display the pHs value of the standard solution.
(4) take out the electrode and rinse it and dry it.
(5) measure the temperature of the sample and adjust the temperature compensation knob of the pH meter to the temperature value.
(6) immerse the electrode into the sample solution, shake it and place it at rest until the steady reading is displayed.