What are the common precautions for pH meter calibration
The laboratory needs more calibration times, because experiments are often done, and the measured solutions are different. At present, the calibration methods are generally divided into one-point calibration, 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 close to the pH value of the test solution should be selected. After the instrument is calibrated with a standard buffer solution during the measurement, it should be checked again with another standard buffer solution with a pH difference of about 3, and the error should not exceed ±0.1. Before changing the standard buffer solution or test solution, the electrodes of the acidity meter should be fully washed with water, and then the water should be sucked up, or washed with the changed standard buffer solution or test solution.
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, and if the sample to be tested is alkaline, please use buffer solutions with pH 7 and 10 to calibrate. Buffer solutions are sold as powdered granules and solutions. Granules have the advantages of long storage time and economy, but they are just inconvenient. The finished solution is easy to use, but it is easy to deteriorate after opening the cover. You can divide the finished solution into small beakers for use.
If you use powdered granules, please make a buffer with 50ml deionized water before calibration. Buffer solutions should be discarded after use for calibration. Therefore, the finished buffer solution should be divided into separate packages for use. Never pour used buffer back into the solution bottle.
When measuring the test product with high pH value, attention should be paid to the problem of alkali error, and if necessary, use a suitable glass electrode for measurement.
To measure the pH value of a weak buffer solution with an acidity meter, first use the potassium hydrogen phthalate standard buffer solution to calibrate the instrument, then measure the test solution, and take the test solution again, until the reading of the pH value does not change within 1 minute. Up to ±0.05; then calibrate the instrument with borax standard buffer solution, and then measure as above; the difference between the readings of the secondary pH value should not exceed 0.1, and take the average value of the secondary readings as its pH value. The water used to prepare the standard buffer solution and dissolve the test product should be freshly boiled cold distilled water, and its pH value should be 5.5-7.0. The standard buffer solution can generally be stored for 2 to 3 months, but if it is found to be turbid, moldy or precipitated, it cannot be used any longer.
