Two-point calibration and operating procedures for ph meter
For precision pH meters, in addition to positioning and temperature compensation adjustments, there is also electrode slope adjustment, which requires calibration with two standard buffer solutions. Generally, pH 6.86 or pH 7.00 is used for "positioning" calibration, and then pH 4.00 (acidic) or pH 9.18 and pH I 0.0l (alkaline) buffer solutions are selected for "slope" calibration based on the acidity and alkalinity of the test solution. The specific operation steps are:
1) Wash and spin dry the electrode, immerse it in a standard solution with pH 6.86 or pH 7.00, and place the instrument temperature compensation knob at the solution temperature. After the indicated value is stable, adjust the positioning knob to make the indicated value of the instrument be the pH value of the standard solution.
(2) Remove the electrode, wash and spin dry it, and immerse it in the second standard solution. After the indicated value is stable, adjust the slope knob of the instrument so that the indicated value of the instrument is the pH value of the second standard solution.
(3) Remove the electrode, wash it and shake it dry, then immerse it in a pH 6.86 or pH 7.00 buffer solution. If the error exceeds 0.02 pH, repeat steps (1) and (2) until the correct pH values can be displayed in both standard solutions without adjusting the knob.
(4) Take out the electrode and shake it dry. Adjust the pH temperature compensation knob to the temperature of the sample solution. Immerse the electrode in the sample solution, shake it, and let it stand still. After the display stabilizes, take a reading.
