Three-point calibration procedures for calibrating pH meters
1. Transfer the standard buffer solutions with pH values of 4.01, 7.00, and 10.01 into clean and dry 50mL small beakers.
2. Press the power button to turn on the pH meter, rinse the electrode and dry it with dust-free paper, then place it in the standard buffer solution with a pH of 4.01. Press the "calibrate" key to the CAL.1 interface, wait for the reading to be stable and the cursor in front of the reading is flashing, press the "digital edit" key to adjust the pH meter reading to the pH value of the standard solution. Then press the "calibrate" key to enter the CAL.2 interface.
3. Rinse the electrode and dry it with dust-free paper, then place it in the standard buffer solution with a pH of 7.00, wait for the reading to be stable and the cursor in front of the reading is flashing, press the "Number Edit" button to adjust the pH meter reading to the standard solution. pH. Then press the "calibrate" key to enter the CAL.3 interface.
4. Rinse the electrode and dry it with dust-free paper, then place it in the standard buffer solution with a pH of 10.01, wait for the reading to be stable and the cursor in front of the reading is flashing, press the "Number Edit" button to adjust the pH meter reading to the standard solution. pH.
5. Press the "measure save/print" key to save the calibration result, and obtain the slope of the straight line after three-point calibration. If the slope of the straight line is within the range of 100±3, and the measured pH values of the other two standard buffer solutions are within the range of ±0.3, the calibration is valid. Otherwise recalibration is required.
6. After using the standard buffer solution, seal it with a parafilm and store it in a dry place for multiple uses.
When the measured pH value of the solution is within a small range (such as 3-8), only two standard buffer solutions with pH 4.01 and 7.00 can be used for calibration.
After the calibration is completed, if the pH meter is used frequently, it should be calibrated every 2 days. The pH meter needs to be recalibrated if:
(1) The electrode is exposed to the air for too long, such as more than half an hour.
(2) After measuring the solution of peracid (pH < 2) or perbasic (pH > 12).
(3) After changing the electrodes.
