What are the key potential factors that affect the pH value
What are the key potential factors affecting pH? Let's focus on the source of potential in pH measurement. In pH measurement, there are a series of different potentials, only one of which is desired (the pH potential). This requires other potentials ('interference potentials') to be very stable, even if they cannot cancel each other out, so that they can be compensated by calibration. As shown in the figure: each potential of the electrode E1—half-cell potential (pH electrode, Ag/AgCL-KCL) E2—inner buffer solution—potential on the inner surface of the glass membrane E3—asymmetric potential of the glass membrane E4—outside the glass membrane Surface change potential (pH potential) E5—flow diffusion potential E6—junction potential E7—half-cell potential (reference electrode, Ag/AgCL-KCL) pH display value is the sum of the above potentials! Among them, E1, E2, E3, and E7 are the stable potentials formed during the electrode manufacturing. Does not affect pH measurement. Only E4, E5, and E6 are affected by the measurement medium. If any potential of E4, E5, and E6 changes, the pH display value will change! During ordinary measurement, E4 directly reflects the pH value of the measured medium, and E5 and E6 have little influence. However, during the pH measurement of high-purity water, the influence of E5 and E6 cannot be ignored, and they are the decisive factors for the inaccurate measurement of the pH value of high-purity water! is the crux of the matter! 1. When the electrode is put into the flow cell, since it is pure water without conductive ions, it takes a certain time for E5 and E6 to stabilize, so the stability and response time of the measured value are relatively long. 2. When the flow rate changes, the balance formed by E5 and E6 is destroyed again, and the measured value can be stabilized only when a new balance is formed again. 3. There is another influencing factor for E6. That is: E6 is greatly affected by the size of the junction area and the way of diffusion. If the junction area of E6 is large and the diffusion is stable, the junction potential is small, and the E6 is stable, so the pH value is stable! precise!