Introduction to pH calibration precautions
The laboratory needs to calibrate more frequently because it requires frequent experiments and the measured solutions are different. At present, the calibration methods are generally divided into one, two point calibration, and three point calibration. The more calibration times, the higher the accuracy, and the more accurate the acidity meter measurement.
When calibrating the instrument before measurement, a standard buffer solution with a pH value close to the test solution should be selected. After calibrating the instrument with a standard buffer solution during the measurement, another standard buffer solution with a pH difference of about 3 should be used to check again, and the error should not exceed ± 0.1. Before replacing the standard buffer or test solution each time, the electrode of the pH meter should be thoroughly washed with water, and then the water should be sucked up completely. Alternatively, the replaced standard buffer or test solution can be used for washing.
To calibrate the pH probe, two buffer solutions are sufficient. If the sample to be tested is acidic, please calibrate the probe with buffer solutions with pH 4 and 7. If the sample to be tested is alkaline, please calibrate with buffer solutions with pH 7 and 10. Buffer solutions are available in powder form as granules and solution products for sale. Granules have the advantages of long storage time and economy, but they are not convenient. The finished solution is easy to use, but it is prone to deterioration after opening the lid. You can divide the finished solution into small beakers and use them separately.
If you use powdered granules, please prepare a buffer solution with 50ml of deionized water before calibration. The buffer solution should be poured out after calibration. Therefore, the finished buffer solution should be packaged separately for use. Never pour the used buffer back into the solution bottle.
When measuring high pH test samples, attention should be paid to the issue of alkali error, and if necessary, suitable glass electrodes should be selected for measurement.
For pH measurement of weak buffer solution by acidimeter, first calibrate the instrument with Potassium hydrogen phthalate standard buffer solution, then measure the test solution, and take the test solution again, until the reading of pH value does not change more than ± 0.05 within 1 minute; Then use borax standard buffer solution to calibrate the instrument, and then measure as described above; The difference between the readings of the secondary pH value should not exceed 0.1, and the average of the secondary readings should be taken as its pH value. The water used to prepare the standard buffer and dissolve the test sample should be freshly boiled cold distilled water, with a pH value of 5.5-7.0. Standard buffer solutions can generally be stored for 2-3 months, but when turbidity, mold, or precipitation are found, they cannot be used again.
