Maintenance technology of acidity meter (detailed introduction)
(1) The main part of the glass electrode is the glass bulb at the lower end. The bulb is extremely thin, so it must not be in contact with hard objects, and special care should be taken when handling and storing it. When installing, the lower end of the glass electrode bulb should be slightly higher than that of the calomel electrode so as not to touch the bottom of the beaker.
(2) The new glass electrode should be soaked in purified water for more than 48 hours before use (a small amount of cotton is built into the beaker), and it is better to soak in purified water when not in use for the next use.
(3) When measuring alkaline solution, it should be tested as quickly as possible, and immediately after the measurement, wash with water and soak in purified water. For the determination of solutions with pH>9, a high-alkali glass electrode (type 231 glass electrode) should be used, because the linear range of the type 221 glass electrode is 0 to 9.5.
(4) After measuring the colloidal solution, protein or dye solution, the glass electrode should be wiped gently with cotton or soft paper dipped in ethanol, then washed with alcohol, and finally washed with water. If the electrode is stained with oil, it should be immersed in alcohol first, then transferred to ether or carbon tetrachloride, then transferred to alcohol, and finally washed with water. If the electrode is stained with dye, it can be washed with dilute bleach solution or dilute hydrogen peroxide solution.
(5) Glass electrodes can be made into different shapes. The spherical and cylindrical shapes are mainly used for liquid media; the flat shape is mainly used for semi-solid media containing water, such as skin, meat, leather, paper, etc.; Into the internal measurement of the medium, such as soil, fruit, etc.
(6) Glass electrode activation: Soak the electrode bulb in 0.1mol/L hydrochloric acid (9mL hydrochloric acid plus purified water to 1000mL) for 24 hours, then wash it with purified water; if the electrode is seriously aging, you can also soak the lower end of the electrode in 4% hydrogen Put in hydrofluoric acid solution for 3-5s, (solution preparation: add water to 4mL hydrofluoric acid to 100mL), then wash with purified water.
(7) When using the calomel electrode, pay attention that the KCl solution should be immersed in the lower opening of the small glass tube inside, and there should be no air bubbles in the bent tube to block the solution.
(8) The calomel electrode is filled with a saturated KCl solution, and there should be a small amount of KCl crystals (use AR-grade KCl crystals).
(9) When calibrating the instrument, try to choose a standard buffer solution with a pH value close to that of the measured solution, and the difference in pH value should not exceed 3 units.
(10) The temperature difference between the standard solution for calibrating the instrument and the measured solution should not exceed 1°C.
(11) During the calibration and measurement process, the beaker should be rotated gently to make the solution uniform.
(12) After the composite electrode is used, it should be immersed in 3mol/L KCl solution.
(13) It is better to prepare the standard buffer solution freshly. It can generally be stored for 2 to 3 months in an airtight container. If turbidity, mold or precipitation are found, it cannot be used any longer.
(14) Use pH 6.86 for positioning calibration, pH 4.00 for slope calibration, and then measure the pH value of the buffer solution at pH 9.18. Whether the difference between the measured value and 9.18 is within the specified error range (such as 0.01 grade pH meter The error is ±0.02pH, the error of the 0.1 grade pH meter is ±0.1pH), and the accuracy of the pH meter can be seen immediately. If the accuracy is unqualified, it can be judged whether there is a problem with the pH meter or the electrode.
(15) The pH meter that has been used or repaired for a long time should be tested for the performance of the pH meter to ensure the accuracy of the measurement. The verification can be carried out according to "JJG119-2005 Laboratory pH (Acidity) Meter Measurement and Verification Regulations".
For more details, please refer to the full text of "Use and Maintenance of Acidity Meter" (Zhao Xiang, Zhao Bing, Wang Guiyan, Liu Jingying, Wang Shaoning, Wang Guoqing)
