What is one-point calibration and two-point calibration of pH meter?
two point calibration
Any pH meter must be calibrated with a pH standard solution before measuring the pH value of the sample. For samples with a measurement accuracy below 0.1, the instrument can be adjusted by one-point calibration. Generally, pH=6.86 or pH=7.00 is used. standard buffer solution. Some instruments are only 0.2pH or 0.1pH, so the instrument only has one 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 the temperature, and adjust the temperature compensation knob to the temperature;
(2) Rinse the electrode with pure water and dry it;
(3) Dip the electrode into the buffer solution and shake it and 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, rinse 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 in the sample solution, shake it and place it still, and display a stable reading.
two point calibration
For the precision grade pH meter, in addition to the "positioning" and "temperature compensation" adjustments, there is also an electrode "slope" adjustment, which needs to be calibrated with two standard buffer solutions. Generally, pH=6.86 or pH=7.00 is used for "positioning" calibration first, and then according to the acid-base condition of the test solution, choose pH=4.00 (acidic) or pH=9.18 or pH=10.01 (alkaline) buffer solution for "slope calibration" , the specific operation steps are as follows:
(1) Clean and dry the electrodes, immerse in the pH=6.86 or pH=7.00 standard solution, and place the temperature compensation knob at the temperature of the solution. After the displayed value is stable, adjust the positioning knob to make the displayed value of the instrument be the pH value of the standard solution.
(2) Take out the electrode, wash it and dry it, and immerse it in the second standard solution. After the displayed value is stable, adjust the slope knob of the instrument so that the displayed value of the instrument is the pH value of the second standard solution.
(3) Clean and dry the electrodes, and then immerse in the pH6.86 or pH7.00 standard solution. If the error exceeds 0.02pH, repeat steps (1) and (2). Until the correct pH value can be displayed without adjusting the knob in the two standard solutions.
(4) Take out the electrode, wash it and dry it, adjust the pH temperature compensation knob to the sample temperature, immerse the electrode in the sample solution, shake it and place it still, and the display will show a stable reading.
