Application of pH Meters in Groundwater pH Testing
1, Calibration method
Turn on the power switch of the instrument, turn the measurement selection switch to the "PH" position, first clean the electrode with distilled water, then insert the electrode into the buffer solution with PH=7, adjust the "temperature" compensator so that the indicated temperature is the same as the temperature of the solution, and then adjust the PH value indicated by the "positioning" regulator to be the same as the PH value of the buffer solution at this temperature. Then remove the electrode inserted into the PH7 buffer solution and clean it with distilled water. Insert the cleaned electrode into a buffer solution with a pH value of 4, so that the temperature indicated by the "temperature" compensator of the instrument is the same as the temperature of the buffer solution. Then adjust the "slope" adjuster to make the pH value displayed by the instrument the same as the pH value of the buffer solution at the temperature of the solution. After calibration, there should be no further changes to the "positioning" and "slope" adjusters, and pH measurement can now be performed. But in general, when the electrode is plugged back into the pH range of 7, if the pH value displayed by the instrument is the same as the buffer solution, it also indicates that the calibration is accurate.
Precautions
1. Re calibrate several aspects
When there is a significant change in solution temperature compared to the calibration temperature; Electrodes that have been away from the solution for too long; Replaced with a new composite electrode; When there are changes in the "positioning" and "slope" adjusters; After measuring pH>12 or pH<2; Measure solutions containing fluoride with acidity below pH 7 or concentrated organic solutions.
2. Instrument maintenance
The input end of the instrument (i.e. composite electrode socket) must be kept highly clean; The composite electrode head is very thin, do not touch with hard objects to prevent electrode damage; There is dirt on the composite electrode head. Use medical cotton to wipe the electrode head or clean it with 0.1N dilute hydrochloric acid; After long-term use, the theoretical percentage of the electrode slightly decreases. The lower end of the electrode should be soaked in 4% HF for 3-5 seconds, washed with distilled water, soaked in a 0.1mol/L HCL solution for a few hours, rinsed with deionized water to restore it; If the composite electrode head cracks or ages (after being stored for more than two years), a new electrode should be replaced. Before using the new electrode, soak it in a 3mol/LKCL solution for 24 hours; When calibrating with buffer solution, ensure its reliability; The LCD display shows "LOBAT" and the battery needs to be replaced; Do not expose the LCD monitor to direct sunlight
3. The input end of the instrument (i.e. composite electrode socket) must be kept highly clean, and the electrode plug should not be frequently removed to prevent dust and high humidity from entering.
4. The electrode must be positioned and calibrated using a standard buffer solution with a known pH value before use.
5. After removing the cap, be careful that the sensitive glass inside the plastic protective barrier does not come into contact with hard objects. Any damage or scratching will cause the electrode to fail.
6. After the measurement is completed, the protective cap should be put on, and a small amount of supplementary liquid (3M/mol KCL) should be placed inside the cap to keep the electrode bubbles moist.
7. The lead out end of the electrode must be kept clean and dry to absolutely prevent short circuits at both ends of the output, otherwise it will cause inaccurate or invalid measurement results.
8. Avoid prolonged immersion in distilled water or protein solutions and acidic fluoride solutions, and prevent contact with organic silicone oil.
