What is one point calibration of pH meters?
Any pH meter must be calibrated by pH Standard solution before measuring the pH value of the sample. For the sample with measurement accuracy of 0.1 and below pH, one point calibration method can be used to adjust the instrument. Generally, pH=6.86 or pH=7.00 standard buffer solution is used. Some instruments themselves only have a pH of 0.2 or 0.1, so they only have a positioning adjustment knob. The specific operation steps are as follows:
(1) Measure the temperature of the standard buffer solution, check the table to determine the pH value at that temperature, and adjust the temperature compensation knob to this temperature;
(2) Rinse the electrode with pure water and shake dry;
(3) Immerse the electrode in the buffer solution and shake it, then place it still. After the reading is stable, adjust the positioning knob to make the instrument display the pH value of the Standard solution;
(4) Take out the electrode and rinse it and shake it dry;
(5) Measure the temperature of the sample and adjust the pH meter temperature compensation knob to this temperature value;
(6) Immerse the electrode in the sample solution, shake it, and then stand still to display a stable reading.
What is the two-point calibration of pH meters?
For precision pH meters, in addition to "positioning" and "temperature compensation" adjustments, there is also an electrode "slope" adjustment, which requires calibration with two standard buffer solutions. Generally, first perform "positioning" calibration with pH=6.86 or pH=7.00, and then select pH=4.00 (acidic) or pH=9.18 or pH=10.01 (alkaline) buffer solution for "slope correction" based on the acidity and alkalinity of the test solution. The specific operation steps are as follows:
(1) Clean and dry the electrode, immerse it in Standard solution with pH=6.86 or pH=7.00, and place the temperature compensation knob at the solution temperature. After the indicated value is stable, adjust the positioning knob so that the indicated value of the instrument is the pH value of Standard solution.
(2) Take out the electrode, wash and 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) Clean and dry the electrode, and then immerse it in the Standard solution of pH6.86 or pH7.00. If the error exceeds 0.02pH, repeat steps (1) and (2). Until the correct PH value can be displayed in both Standard solution without adjusting the knob.
(4) Take out the electrode, wash it and shake it dry. Adjust the pH temperature compensation knob to the sample temperature, immerse the electrode in the sample solution, shake it, and then stand still. After the display is stable, the reading will be stable
