The pH electrode for the ph meter has the following features:
⑴ asymmetric potential: when the electrode of the internal and external reference electrode, the internal and external reference solution are the same, in theory, the battery electromotive force should be equal to zero, but in fact there are always a few millivolts to dozens of millivolts of potential difference, indicating that the glass bulb Inside and outside the two interfaces are asymmetric, this potential difference is called asymmetric potential. Asymmetric potential and the bubble blowing process, but also with the use of the ball surface erosion or contamination related to the actual use of the special meter can be used to eliminate it.
⑵ Zero Potential: The zero potential of the pH electrode refers to the pH of the solution when the potential of the pH measuring cell is zero. It depends on the pH value of the internal reference solution and the chloride ion concentration. If the internal reference solution is 0.025mol / L mixed phosphate solution, the electrode zero potential pH value is greater than or less than the electrode zero potential pH, the electrode polarity will change.
⑶ internal resistance: the internal resistance of the electrode is mainly determined by the internal resistance of the glass bulb film, which depends on the composition and thickness of the glass, the resistance is generally tens of megaohms. And increases exponentially as the temperature decreases (7 ° C for each drop, double the internal resistance, for example 50 megohms for 28 ° C and 800 megohms for 0 ° C). High internal resistance of the electrode on the meter input impedance and insulation requirements of high shielding, low resistance of the electrode as well.
⑷ alkali error and acid error: When the measured acidity and alkalinity of the solution increases, the electrode potential and the solution pH will deviate from the linear relationship, this deviation is called the base error and acid error. The alkali error is due to the fact that in the solution of low hydrogen ion concentration, the response of the electrode film depends not only on the hydrogen ion concentration but also on the concentration of alkali metal ions in the solution. The alkali error makes the measured pH value lower than the actual value. Acid error occurs in the lower pH range (pH <1-2) and the acid error causes the pH measurement to be higher than the actual value.