Principle of pH electrode and precautions for use and mainte

Principle of pH electrode and precautions for use and maintenance

 

Core tips：

PH electrode, also known as pH probe, is the part of pH meter in contact with the measured substance, which is used to measure the electrode potential。

 

The electrode used in potentiometric analysis is called galvanic cell. Galvanic cell is a system, its role is to make chemical reaction energy into electrical energy. The voltage of this battery is called electromotive force (EMF). The EMF consists of two and a half cells. One half cell is called the measuring electrode, whose potential is related to the specific ionic activity; the other half cell is the reference half cell, usually called the reference electrode, which is generally connected with the measuring solution and connected with the measuring instrument. The most familiar and commonly used pH indicating electrode is glass electrode. Bell's T225 electrode is suitable for the measurement of pure water and high-purity water in pharmaceutical pulp, paper making, electroplating, biopharmaceutical, power plant and other industries. It is a glass tube with a pH sensitive glass film blown at the end. The tube was filled with 3 mol / L KCl buffer solution containing saturated AgCl, and its pH value was 7. The potential difference existing on the two sides of glass film reflecting pH value was measured by Ag / AgCl conduction system。

 

Precautions for pH electrode use and maintenance：

1．The electrode must be calibrated with a standard buffer solution with known pH value before measurement (at least 2 points)。

2．Before the next operation after each calibration and measurement, the electrode should be cleaned with distilled water or deionized water, and then cleaned with the measured solution。

3．When removing the electrode sheath, the sensitive glass bubble of the electrode should be avoided to contact with hard objects, because any damage or brushing will make the electrode invalid。

4．After measurement, put a small amount of saturated KCl liquid on the electrode protection sleeve in time to keep the electrode bulb wet. Do not soak it in distilled water。

5．The external reference solution of the composite electrode is 3mol / L potassium chloride solution. The additional fluid can be added from the upper end of the electrode. When the composite electrode is not used, the rubber plug is covered to prevent the fluid from drying up. The online pH electrode is 1 gel, so no electrolyte is needed。

6．The lead out end of the electrode must be kept clean and dry to absolutely prevent short circuit at both ends of the output, otherwise it will lead to measurement inaccuracy or failure。

7．The electrode should be matched with pH meter & Ge; 3 & times; 1011 & omega; with high input impedance to keep good characteristics。

8．The electrode should avoid long-term immersion in distilled water, protein solution and acidic fluoride solution。

9．Avoid contact with silicone oil。

10．If the slope of the electrode decreases slightly after long-term use, the lower end of the electrode can be soaked in 4% HF hydrofluoric acid for (3 ~ 5) s, cleaned with distilled water, and then soaked in 0.1mol/l hydrochloric acid solution to renew it. It is better to replace the electrode。

11．If the electrode is passivated due to the substance in the measured solution that is easy to contaminate the sensitive bulb or block the liquid junction, the slope will decrease and the reading will be inaccurate. In case of this phenomenon, the electrode should be renewed by cleaning with appropriate solution according to the nature of the pollutant。