Is there a big error if the pH meter is used directly without calibration?
1. One-point calibration of acidimeter
Any pH meter must be calibrated with a pH standard solution before it can measure the pH value of the sample. For samples with a measurement accuracy below 0.1 pH, the instrument can be adjusted using a one-point accuracy method. Generally, pH 6.86 or pH 7 is used. 00 standard buffer. Some instruments have an accuracy of only 0.2pH or 0.lpH, so the instrument only has one positioning adjustment knob. The specific steps are as follows:
(1) Measure the temperature of the standard buffer solution, look up the table to determine the pHs value at this temperature, and adjust the temperature compensation knob to this temperature.
(2) Rinse the electrode with pure water and spin dry.
(3) Dip the electrode into the buffer solution and shake it, then place it still. After the reading is stable, adjust the positioning knob so that the instrument displays the pH value of the standard solution.
(4) Take out the electrode, rinse and spin dry. (5) Measure the sample temperature and adjust the pH meter temperature compensation knob to the temperature value
2. Two-point calibration of acidometer
For precision-grade pH meters, in addition to ¨positioning¨ and ¨temperature compensation¨ adjustments, there is also an electrode ¨slope¨ adjustment, which requires calibration with two standard buffers. Generally, pH 6.86 or pH 7.00 is used for positioning calibration first, and then according to the acidity and alkalinity of the test solution, pH 4.00 (acidic) or pH 9.18 and pHI 0.0l (alkaline) buffer solution is used for slope calibration. Correction. The specific steps are:
(1) Wash and dry the electrode, immerse it in the pH6.86 or pH7.00 standard solution, and place the instrument temperature compensation knob at the solution temperature. After the indication value is stable, adjust the positioning knob so that the instrument indication value is the pHs value of the standard solution.
(2) Take out the electrode, wash it, spin it dry, and immerse it in the second standard solution. After the indication value is stable, adjust the slope knob of the instrument so that the instrument indication value is the pHs value of the second standard solution.
(3) Take out the electrode, wash it and spin it dry, and then immerse it in the pH6.86 or pH7.00 buffer solution. If the error exceeds 0.02pH, repeat steps (1) and (2) until the correct pHs can be displayed in both standard solutions without adjusting the knob.
(4) Take out the electrode and spin 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 place it still until the reading is stable.
3. The third point calibration of pH meter
No matter what kind of pH meter it is, the point pH=7 must be calibrated, and when calibrating at two points, the point pH=7 must be calibrated first. When doing calibration, start from 7.0. The selected standard solution is related to the pH value of the solution to be measured, so that the pH value of the solution can fall within the calibration pH range. Generally, two points can meet the requirements. If the requirements are very high, the third point will be considered. Some instruments can calibrate three points and have optional modes. You can use this mode directly. For some, two-point and two-point proofreading is generally used, that is, proofreading twice.
