pH meter maintenance issues
maintainance
1. Storage of pH glass electrode
Short term: store in buffer solution with pH=4;
Long-term: Store in buffer solution with pH=7.
2. Cleaning of pH glass electrode
Contamination of the glass electrode bulb may lengthen the electrode response time. Wipe away dirt with CCl4 or soap, then soak in distilled water for a day and night before continuing to use. When the pollution is serious, it can be soaked in 5% HF solution for 10 to 20 minutes, rinsed immediately with water, and then immersed in 0.1N HCl solution for one day and night before continued use.
3. Treatment of glass electrode aging
The aging of glass electrodes is related to the gradual change of the glue layer structure. The old electrode had a sluggish response, high membrane resistance, and low slope. Using hydrofluoric acid to etch away the outer adhesive layer can often improve electrode performance. If this method can be used to regularly remove the inner and outer rubber layers, the life of the electrode will be almost unlimited.
4. Storage of reference electrode
The best storage solution for silver-silver chloride electrodes is saturated potassium chloride solution. High-concentration potassium chloride solution can prevent silver chloride from precipitating at the liquid junction and keep the liquid junction in working condition. This method is also applicable to the storage of composite electrodes.
5. Regeneration of reference electrode
Most of the problems that occur with the reference electrode are caused by clogging of the liquid junction, which can be solved by the following methods:
(1) Soaking liquid junction: 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 and remove the crystals at the ends of the electrodes.
(2) Ammonia immersion: When the liquid junction is blocked by silver chloride, it can be leached with concentrated ammonia water. The specific method is to clean the electrode, drain the liquid and then immerse it in ammonia water for 10 to 20 minutes, but do not let ammonia enter the inside of the electrode. Take out the electrode, wash it with distilled water, refill the electrode and continue using it.
(3) Vacuum method: Put the hose around the liquid junction of the reference electrode, use a water flow suction pump to suck the partially filled liquid through the liquid junction, and remove mechanical obstructions.
(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 grinding sand particles to be stuffed into the liquid junction. Causes destructive blockage.
examine
1. General inspection methods of glass electrodes
(1) Check zero potential
Set the pH meter to the "mV" measurement position, insert the glass electrode and the reference electrode into the buffer solution with pH = 6.86, and the reading of the instrument should be approximately -50~50mV.
(2) Check the slope
Follow (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 indicators.
