Brief procedure for calibrating a ph meter
I. One-point calibration of acidity meter
Any kind of pH meter must be calibrated by the pH standard solution before measuring the pH value of the sample, for the measurement accuracy of 0.lpH samples, you can use a little bit of polar calibration method to adjust the instrument, generally choose pH6.86 or pH7.00 standard buffer. Some instruments have only 0.2pH or 0.lpH accuracy, so the instrument is only equipped with a ¨position¨ adjustment knob. The specific operation steps are as follows:
(1) Measure the temperature of the standard buffer, check the table to determine the pHs value at that temperature, and adjust the temperature compensation knob to that temperature.
(2) Rinse the electrode with pure water and shake it dry.
(3) Immerse the electrode in the buffer solution and shake it, then place it in a stationary position. When the reading is stable, adjust the positioning knob so that the instrument displays the pH value of the standard solution.
(4) Remove the electrode and rinse and shake dry.
(5) Measure the temperature of the sample and adjust the temperature compensation knob of the pH meter to the temperature value.
Two-point calibration of the pH meter
For precision level pH meter, in addition to ¨ positioning ¨ and ¨ temperature compensation ¨ adjustment, but also has an electrode ¨ slope ¨ adjustment, it will need to be calibrated with two standard buffer. Generally the first pH6.86 or pH7.00 for ¨ positioning¨ calibration, and then according to the acid-base situation of the test solution, the choice of pH4.00 (acidic) or pH9.18 and pHI0.0l (alkaline) buffer solution for the ¨ slope¨ calibration. The specific operation steps were:
(1) The electrode is washed and dried, immersed in pH6.86 or pH7.00 standard solution, and the instrument temperature compensation knob is placed at the solution temperature. When the display value is stable, adjust the positioning knob so that the instrument display value is the pHs value of the standard solution.
(2) Remove the electrode, wash and dry, immersed in the second standard solution. When the value is stable, adjust the slope knob of the instrument so that the value of the instrument is the pHs value of the second standard solution.
(3) Remove the electrode, wash and dry it, and then immerse it in pH 6.86 or pH 7.00 buffer solution. If the error is more than 0.02 pH, repeat steps (1) and (2) until the correct pHs value is displayed in both standard solutions without adjusting the knob.
(4) Remove the electrode and shake dry, adjust the pH temperature compensation knob to the temperature of the sample solution, immerse the electrode in the sample solution, shake and then stand still, display the reading after stabilisation.
Third, the third point of calibration of the pH meter
Regardless of what kind of pH meter, pH = 7 this point must be corrected, and in the two-point calibration should be corrected first pH = 7 this point. Do the calibration from 7.0 to start, select the standard solution and to determine the pH value of the solution, so that the pH value of the solution can fall in the calibration of the PH range. Generally two points can be used to meet the requirements, if the requirements are very high, before considering the third point. Some instruments can calibrate three points, there are modes to choose, you can use the mode directly. Some do not have, generally using two-point two-point calibration, that is, calibration twice.
