How to Correctly Understand the Methods of Using pH Meters and the Maintenance Electrodes of pH Meters
① The voltage and frequency of the power supply must comply with the data indicated on the instrument nameplate, and it must be well grounded, otherwise the pointer may be unstable during measurement
② The instrument is equipped with glass electrodes and calomel electrodes. Clamp the bakelite cap of the glass electrode onto the small clip of the electrode clamp. Clamp the metal cap of the calomel electrode onto the large clamp of the electrode clamp. The height of the two electrodes can be adjusted using the support screws on the electrode clamp.
③ Glass electrodes must be soaked in distilled water for at least 24 hours before initial use. It should also be soaked in distilled water when not in use.
④ Before initial use, calomel electrode shall be immersed in saturated Potassium chloride solution, and shall not be soaked with glass electrode in distilled water. When not in use, it is also immersed in saturated Potassium chloride solution or covered with a rubber cap with the pores at the lower end of the calomel electrode.
Secondly, calibration
① Turn the "pH mv" switch to the pH position.
② Turn on the power and the indicator light will light up. Warm up for 30 minutes.
③ Take a small beaker containing distilled water and gently remove excess water droplets from the glass electrode with filter paper. Pour a selected standard buffer solution with a known pH into a small beaker. Immerse the electrode. Pay attention to immersing the small ball at the end of the glass electrode and the capillary pores of the calomel electrode in the solution. Gently shake the small beaker to make the solution in contact with the electrode uniform.
④ According to the pH of the standard buffer, turn the range switch to positions 0-7 or 7-14.
⑤ Adjust the temperature control knob so that the temperature indicated by the knob is the same as the room temperature.
⑥ Adjust the zero point so that the pointer points at pH7.
⑦ Gently press or slightly rotate the reading switch to make it stick. Adjust the positioning knob so that the pointer is exactly at the pH value of the standard buffer. Release the reading switch and repeat the operation until the value stabilizes.
⑧ After calibration, do not rotate the positioning knob again, otherwise it needs to be recalibrated. Remove the standard solution beaker and rinse the electrode with distilled water.
Finally, measurement
① Suck up excess water droplets on the electrode or rinse twice with the tested solution, then immerse the electrode in the tested solution and gently rotate or shake the small beaker to make the solution evenly contact the electrode.
② The temperature of the tested solution should be the same as that of the standard buffer solution.
③ Adjust the zero position, press the reading switch, and the value indicated by the pointer is the pH of the liquid to be measured. If the pointer reading exceeds the scale when measuring within the range of pH 0-7, the range switch should be placed at pH 7-14 before measurement.
④ After the measurement is completed and the reading switch is released, the pointer must point to pH7, otherwise readjust.
⑤ Turn off the power, rinse the electrodes, and soak them according to the aforementioned method.
When emphasizing the use of pH meter methods, it is also important to have a correct understanding of the electrode usage of pH meters. At present, the electrodes used in the laboratory are all composite electrodes, which have the advantages of being easy to use, not affected by oxidizing or reducing substances, and having a fast equilibrium speed. When using, remove the rubber sleeve on the electrode filling port and the rubber sleeve at the lower end to maintain the hydraulic pressure difference of Potassium chloride solution in the electrode. Below is a brief introduction to the use and maintenance of electrodes:
1. When the composite electrode is not used, it can be fully immersed in 3M Potassium chloride solution. Do not use washing
1. When the composite electrode is not used, it can be fully immersed in 3M Potassium chloride solution. Do not soak with detergent or other absorbent reagents.
2. Before use, check the bulb on the front end of the glass electrode. Under normal circumstances, the electrode should be transparent and free from cracks; The bulb should be filled with solution and no bubbles should exist.
When measuring solutions with high concentrations, try to shorten the measurement time as much as possible and carefully clean them after use
Wash to prevent the measured solution from adhering to the electrode and contaminating it.
4. After cleaning the electrode, do not use filter paper to wipe the glass film. Instead, use filter paper to absorb and dry it to avoid damaging the glass film, preventing cross contamination, and affecting measurement accuracy.
5. During measurement, pay attention to the silver Silver chloride internal reference electrode of the electrode should be immersed in the chloride buffer solution in the bulb to avoid the digital jump phenomenon in the electrometer display part. When using, be careful to gently shake the electrode a few times.
6. Electrodes should not be used in strong acids, alkalis, or other corrosive solutions.
7. It is strictly prohibited to use it in dehydrating media such as anhydrous ethanol, Potassium dichromate, etc.
