why do we calibrate a ph meter

A pH calibration is the procedure of adjusting the pH meter by measuring solutions of known pH values. Why you need to calibrate The characteristic of a pH electrode will change with time due to And even a pH electrode would be stable over time, pH electrodes cannot be produced with identical characteristics. In practice the response of a real pH sensor does not exactly follow the This difference between the theoretical and actual behavior of a pH
electrode must be compensated for.


A calibration is required to match
the pH meter to the current characteristics of the used pH sensor. How to perform a calibration is performed by measuring a known, well defined solution, a so-called
Two-point calibration The most common pH electrode calibration method is the two-point calibration. During a two-point calibration, the microprocessor based pH meter determines the and for the actual pH electrode. This information is then used to adjust the mV/pH-equation of the pH meter to match the characteristic of the electrode in use.


The two-point calibration is also called bracketing calibration, since the two calibration points should bracket the range of values that will be measured. Multi-point calibration To achieve the best possible accuracy, the calibration should cover the range of the desired measurement values. If the readings go beyond the calibrated range, the pH meter assumes linearity and simply extrapolates the value to be displayed.


The true value may be slightly different. More advanced pH meters will let the user calibrate at three, four or five and even higher numbers of pH values. A multi-point calibration mean, in comparison to a two-point calibration, that you can calibrate your pH tester on both sides of the zero point (pH 7. 00). This will expand your pH measurement range without the need of recalibrating. Calibration interval pH calibration must be repeated periodically.


The time interval between calibrations depends on a number of factors, Prepare your buffers. You will generally need more than one buffer for calibrating a pH meter. The first will be a БneutralБ buffer with a pH of 7, and the second should be near the expected sample pH, either a pH of 4 or 9. 21. Buffers with a higher pH (9. 21) are best calibrated for measuring bases, whereas buffers with a low pH (4) are best for measuring acidic samples.


Once you have chosen your buffers allow them to reach the same temperature, as pH readings are temperature dependent. Pour your buffers into individual beakers for calibration. Check with your pH meter manufacturer, or current educational or professional institution, about acquiring pH buffer solutions. Buffers should be kept in a beaker for no longer than two hours. Do not pour used buffer back into its original container.