Some basic knowledge of pH electrode maintenance and inspection on pH meter
With the widespread use of pH meters in various industries such as industry, laboratories, and light industry. As follows, the PH meter has become an indispensable part of production and laboratories. It has replaced the status of PH test paper in the industry with the characteristics of system, measurement precision, and high precision. The pH electrode is the main component of the pH meter. In a sense, the use of the pH electrode can directly affect the use of the pH meter. Therefore, we must ensure that the pH electrode is normal during use, so we need to understand correctly And use the pH electrode, and the pH electrode should be maintained and tested from time to time. Only in this way, our products will not break down during use.
(1) Maintenance of pH electrode
1. Storage of pH glass electrodes (most pH meters are equipped with glass electrodes)
Short-term: store in buffer solution with pH=4;
Long-term: Store in buffer solution with pH=7.
2. Cleaning of the pH glass electrode. Pollution of the bulb of the glass electrode may prolong the response time of the electrode. The dirt can be wiped off with CCl4 or soap solution, and then soaked in distilled water for a day and night before continuing to use. When the pollution is serious, it can be immersed in 5% HF solution for 10-20 minutes, rinsed with water immediately, and then immersed in 0.1N HCl solution for a day and night before continuing to use.
3. Glass electrode aging treatment The aging of glass electrodes is related to the gradual change of the glue layer structure. Older electrodes have sluggish response, high membrane resistance, and low slope. Etching off the outer adhesive layer with hydrofluoric acid often improves electrode performance. If this method can be used to regularize the inner and outer adhesive layers, the life of the electrode is almost unlimited.
4. Storage of reference electrode The best storage solution for silver-silver chloride electrode is saturated potassium chloride solution. High-concentration potassium chloride solution can prevent silver chloride from precipitating at the liquid junction and maintain the liquid junction at work. state. This method is also applicable to the storage of composite electrodes.
5. Regeneration of the reference electrode Most of the problems of the reference electrode are caused by the blockage of the liquid junction, which can be solved by the following methods:
(1) Junction of soaking solution: use a mixture of 10% saturated potassium chloride solution and 90% distilled water, heat to 60-70°C, immerse the electrode about 5cm, and soak for 20 minutes to 1 hour. This method can dissolve the crystals at the end of the electrode.
(2) Ammonia soaking: When the liquid junction is blocked by silver chloride, it can be soaked with concentrated ammonia water. The specific method is to clean the inside of the electrode, drain the liquid and immerse it in ammonia water for 10-20 minutes, but do not let the ammonia water enter the inside of the electrode. Take out the electrode and wash it with distilled water, and then add the filling liquid again and continue to use it.
(3) Vacuum method: put the hose around the liquid junction of the reference electrode, use a water flow suction pump, and the liquid in the suction part passes through the liquid junction to remove mechanical blockages.
(4) Boiling liquid junction: The liquid junction of the silver-silver chloride reference electrode is immersed in boiling water for 10 to 20 seconds.
Note that the electrode should be cooled to room temperature before the next boil.
(5) When the above methods are ineffective, the mechanical method of sandpaper grinding can be used to remove the blockage. This method may cause the grit under grinding to plug into the liquid junction. cause a one-time blockage.
(2) Inspection of pH electrode
1. General inspection method of glass electrode
(1) Check the zero potential and set the pH meter to the "mV" measurement range. Insert the glass electrode and the reference electrode into the buffer solution with pH=6.86. The reading of the instrument should be about -50~50mV.
(2) Check the slope: Connect to (1), then measure the mV value of the buffer solution with pH=4.00 or pH=9.18, and calculate the slope of the electrode. The relative slope of the electrode should generally be combined with the technical index.
Notice:
1) The method for checking the zero potential value of electrodes is only for glass electrodes with an equipotential point of 7. If the equipotential point of the glass electrode is not 7, it will be different.
2) For some pH meters, if the calibration adjustment can meet the requirements, and the above inspection results are not out of range, the electrode can be used.
3) For some smart pH meters, you can directly refer to the zero potential and slope values obtained from the calibration results of the instrument.
2. Inspection method of reference electrode
(1) Internal resistance inspection method: Use a laboratory conductivity meter. One end of the electrode socket of the conductivity meter is connected to a reference electrode, and the other end is connected to a metal wire. The reference electrode and the metal wire are immersed in the solution at the same time. The resistance should be less than 10kΩ. If the internal resistance is too large, it means that the liquid junction is blocked and should be dealt with.
(2) Electrode potential check: take a good reference electrode of the same model and the reference electrode to be tested and connect them to the input ends of the pH meter, and then insert KCl solution (or buffer solution with pH=4.00) at the same time, and measure The potential difference should be -3 ~ 3mV, and the potential change should be less than ± 1mV. Otherwise, the reference electrode should be replaced or regenerated.
(3) Visual inspection: the silver-silver chloride wire should be dark brown, if it is off-white, it means that the silver chloride has been partially dissolved.
