Use, maintenance and upkeep of pH electrodes
1. Use of pH electrodes
Currently, most of the pH meter electrodes used in the laboratory are composite electrodes. Its advantages are easy to use, unaffected by oxidation-reduction substances, and fast equilibrium speed. The following precautions should be taken when using:
(1) During use, the rubber sleeve and the lower rubber sleeve of the pH electrode filling port shall be removed to maintain the pressure difference of Potassium chloride solution in the electrode. Before use, check the front end of the glass electrode bulb. Under normal circumstances, the electrode should be transparent and free of cracks. The bulb should be filled with solution and there should be no bubbles present.
(2) Generally, a two-point calibration is adopted, with 6.86pH () as the first point and 4.00pH () or 9.18pH () as the second point (note that the calibration value should be consistent with the standard value of the Standard solution at the actual measured temperature). During the calibration process, try to stabilize the pH value as much as possible before pressing the confirm button.
(3) When the pH electrode performance is generally good, the slope after calibration should be above 98%, and the performance should slightly decrease by over 95%. If it is below 90%, it is recommended to replace the electrode.
(4) In the calibrated state, the slow and unstable reaction is a manifestation of the decrease in pH electrode performance.
(5) The pH composite electrode is not suitable for measuring organic substances, oils, viscous substances, etc.
(6) The most common problem with the use of pH composite electrodes is external reference. The blockage at the liquid interface of the electrode is the main cause of error.
(7) When measuring the value of a solution using a pH electrode, it should be stirred thoroughly, otherwise the reaction will be slow.
(8) In winter, when the ambient temperature reaches freezing point, the pH electrode cannot be used and is prone to cold explosion. It is recommended to use it above.
2. Maintenance of pH electrodes
(1) The connectors and sockets connecting pH electrodes should be kept clean, dry, non polluting, and ensure good contact. When there is pollution, 99% industrial alcohol can be used to wipe.
(2) The pH electrode used for the first time (no solution in the sheath) or stopped for a long time must be soaked in 3mol/L Potassium chloride solution for 24 hours before use.
(3) When measuring solutions with high concentrations, try to shorten the measurement time as much as possible, and carefully clean them after use to prevent the measured solution from adhering to the pH electrode and contaminating it.
(4) The electrode should avoid long-term immersion in distilled water, protein solution, and acidic fluoride solution, and should avoid contact with organic silicone oil.
(5) After measurement, the pH electrode shall be inserted into the sheath containing Potassium chloride solution, and the amount of Potassium chloride solution in the electrode rod shall be frequently observed. It shall be added in time, generally not less than half. Plug the upper plug when not measuring.
