Do you have to calibrate the pH calibration?
pH measurement usually colorimetry (pH paper or cuvette) and electrode method two. Colorimetric certainly not calibration, and the electrode method must be calibrated, because the electrode method pH measurement is the unknown solution and the known pHs standard solution in the measurement of the role of the battery compared to the electrode method is pH measurement of the "operational definition "The decision.
pH meter due to the design of different types and many different types of operation steps are different, and therefore the operation of the pH meter should be strictly in accordance with the instructions for use correctly. In specific operations, calibration is an important step in the pH meter's operation. The data in Table 1 is an accuracy of 0.01. The calibration of the calibrated pH value of the calibrated pH meter after unmetered and calibrated measurements shows the importance of the calibration.
Although many types of pH meters are used, the calibration method uses a two-point calibration method that selects two standard buffers: one is pH7 standard buffer and the second is pH9 standard buffer or pH4 standard buffer. First use pH7 standard buffer to locate the electrometer, and then select the second standard buffer according to the pH value of the solution to be tested. If the test solution is acidic, the choice of pH4 standard buffer; if the test solution was alkaline, the choice of pH9 standard buffer. In the case of a manually adjusted pH meter, several times between two standard buffers should be repeated until the Zero and Positioning (slope) knobs are not adjusted and the pH meter accurately shows the pH of both standard buffers. The calibration process is completed. After that, the zero and positioning knobs should not be moved during the measurement. If the intelligent pH meter, then do not need to repeatedly adjust, because of its internal storage of several standard pH buffer to choose from, and can automatically identify and automatically calibrate. But pay attention to the standard buffer selection and the accuracy of its preparation. The intelligent 0.01-level pH meter generally has three to five kinds of standard buffer pH values, such as Kohler's KL-016 pH meter.
Second, pay special attention to the temperature of the solution to be measured before calibration. So that you can select the standard buffer correctly and adjust the temperature compensation knob on the electrometer panel to match the temperature of the solution under test. Different temperatures, the standard buffer solution pH is not the same.
Calibration work is completed, the use of frequent pH meter generally within 48 hours without re-calibration of the instrument. If you encounter any of the following conditions, the instrument needs to be recalibrated:
⑴ solution temperature and calibration temperature have a greater difference.
⑵ electrode exposed in the air for too long, such as more than half an hour.
⑶ positioning or slope regulator is malfunctioning;
⑷ measured acid (pH <2) or over-alkali (pH> 12) solution;
⑸ replaced after the electrode;
⑹ When the pH value of the solution under test is not in the middle of the selected solution at the two point calibration, and further away from 7pH.
1.the measurement time should be specified in the instructions of the instrument calibration.
2. calibration should pay attention to:
Standard buffer solution temperature as close as possible to the measured solution temperature.
Positioning standard buffer solution should be as close to the measured solution pH. Or two calibration, should try to make the pH value of the solution in the two standard buffer solution interval.
After calibration, the electrode immersed in the standard buffer solution should be washed with water, because the buffer solution buffer effect, brought into the test solution, resulting in measurement error.
3.record the pH value of the measured solution should be recorded at the same time the measured temperature of the solution, because the value of leaving the temperature, pH almost meaningless. Although most pH meters have a temperature compensation function, they only compensate for the electrode's response, that is, only half-compensation, without simultaneous temperature compensation of the measured solution, ie full compensation.
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