Guidelines for Proper Use and Maintenance of pH Meters
I. Proper Use and Maintenance of pH Electrodes
Currently, pH electrodes used in laboratories are all combination electrodes. They feature convenient operation, immunity to oxidizing or reducing substances and fast equilibrium speed. Before use, remove both the rubber sleeve covering the filling hole and the rubber cap at the bottom of the pH electrode to maintain the hydraulic pressure difference of the potassium chloride solution inside the electrode. A brief introduction to electrode operation and maintenance is given below:
① When the combination electrode is not in use, fully immerse it in 3M potassium chloride solution. Never soak it in detergent or other water-absorbing reagents.
② Before use, inspect the bulb at the tip of the glass electrode. Under normal conditions, the electrode shall be transparent and crack-free; the bulb shall be fully filled with liquid without air bubbles.
③ When measuring high-concentration solutions, minimize the measurement duration and thoroughly clean the electrode after use to prevent the measured liquid from adhering to and contaminating the electrode.
④ After cleaning the electrode, do not wipe the glass membrane with filter paper. Instead, blot it dry with filter paper to avoid damaging the thin glass film and cross-contamination, which will affect measurement accuracy.
⑤ During measurement, ensure that the silver-silver chloride internal reference electrode is immersed in the chloride buffer solution inside the bulb to prevent erratic digital readings on the meter. Gently shake the electrode a few times before use.
⑥ The electrode shall not be used in strong acid, strong alkali or other corrosive solutions.
⑦ It is strictly prohibited to use the electrode in dehydrating media such as anhydrous ethanol and potassium dichromate.
II. Preparation and Storage of Standard Buffer Solutions
① pH standard materials shall be stored in a dry place. For example, mixed phosphate pH standard materials will deliquesce under high air humidity. Once deliquesced, the pH standard material cannot be used.
② Double-distilled water or deionized water shall be used for preparing pH standard solutions. Ordinary distilled water is acceptable for 0.1-grade pH meters.
③ Use a small beaker for dilution during preparation to reduce the loss of pH standard solution adhering to the beaker wall. The plastic bag or other container holding the pH standard material shall be emptied completely and rinsed several times with distilled water. All rinsate shall be poured into the prepared pH standard solution to guarantee accuracy.
④ The prepared standard buffer solution can generally be stored for 2 to 3 months. Discard the solution if turbidity, mold or precipitation is observed.
⑤ Alkaline standard solutions shall be hermetically stored in polyethylene bottles to prevent carbon dioxide ingress, which forms carbonic acid and lowers the pH value.
