Does the pH meter use the error directly, without calibrating first?
1. One-point calibration of acidity meter
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 0.1pH, the instrument can be adjusted with a one-point accurate method. Generally, pH6.86 or pH7. 00 standard buffer. Some instruments have an accuracy of only 0.2pH or 0.lpH, so the instrument only has 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 pHs value at the temperature, and adjust the temperature compensation knob to the temperature. (2) Rinse the electrode with pure water and shake dry. (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 sample temperature, and adjust the temperature compensation knob of the pH meter to the temperature value
2. Two-point calibration of acidity meter
For precision grade pH meters, in addition to ¨positioning¨ and ¨temperature compensation¨ adjustments, there is also an electrode ¨slope¨ adjustment, which requires two standard buffer solutions for calibration. Generally, pH6.86 or pH7.00 is used for ¨positioning¨ calibration first, and then according to the acid-base condition of the test solution, pH4.00 (acidic) or pH9.18 and pHI0.0l (alkaline) buffer solution is selected for ¨slope¨ Correction. The specific operation steps are:
(1) Clean and dry the electrode, immerse in pH6.86 or pH7.00 standard solution, and place the temperature compensation knob of the instrument at the temperature of the solution. After the displayed value is stable, adjust the positioning knob to make the instrument display the pHs value of the standard solution.
(2) Take out the electrode, wash 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 pHs value of the second standard solution.
(3) Take out the electrode, wash it and dry it, then immerse it in 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 the two standard solutions without adjusting the knob.
(4) Take out the electrode and dry it, 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, and the reading will display after stabilization.
3. The third point calibration of the pH meter
No matter what kind of pH meter, the point of pH=7 must be calibrated, and the point of pH=7 must be calibrated first during the two-point calibration. When doing calibration, start from 7.0, and 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 calibrated pH range. Generally, two points can be used to meet the requirements. If the requirements are very high, the third point should be considered. Some instruments can calibrate three points, and there is an optional mode, which can be used directly. For some that don't, two-point two-point proofreading is generally used, that is, proofreading twice.
