The principle of ORP meter

1, the traditional method of determination of redox potential

For a long time, redox potential was measured directly by platinum electrode. That is, the platinum electrode and the reference electrode are directly inserted into the medium for measurement. The ORP electrode is an electrode that can absorb or release electrons on the surface of its sensitive layer. The sensitive layer is an inert metal, usually made of platinum and gold. The reference electrode is a saturated calomel electrode or a silver/silver chloride electrode.

2, the characteristics of the traditional determination of redox potential

The traditional determination of redox potential is very simple, it consists of ORP composite electrode and mV meter. However, it takes a long time to reach the equilibrium potential value. Especially when the weak equilibrium system is measured, since the platinum electrode is not absolutely inert, an oxide film or other substances may be adsorbed on the surface thereof. Affects the electron exchange rate of each redox couple on the platinum electrode, so the establishment of the equilibrium potential is extremely slow. It takes several hours or even one or two days in some media, and the measurement error is very large, usually 40-100 mV. In the ORP assay, artificially specify a reading time, such as 5 minutes, or 10 minutes, or 30 minutes. When publishing articles or submitting data, the reading time must be identified.

3, to obtain a relatively accurate method of measurement

If the platinum electrode's surface properties and the dynamics of the electrode potential are fully considered, for a complex medium, if a depolarization method is used to measure the redox potential, a more accurate result can be obtained in less than 2 minutes. This result is equivalent to a conventional assay method that equilibrates the potential for 48 hours, usually less than 10 mV or better.

4, redox potential depolarization assay

The polarization voltage was adjusted to 600-750 mV. A silver-silver chloride electrode was used as an auxiliary electrode. The platinum electrode was connected to the positive terminal of the power supply, and the anode was polarized (freely selected in a polarization time of 5-15 seconds). Then the polarization was cut off. The power supply (depolarization time is freely selected over 20 seconds), and the potential of the platinum electrode (for calomel electrode) is monitored during depolarization. There is a linear relationship between the electrode potential E (millivolts) and the logarithm of the depolarization time logt. Cathode polarization and subsequent depolarization monitoring were performed in the same way. The intersection of the anode depolarization curve and the extension line of the cathode depolarization curve corresponds to the equilibrium potential. The equation for the two curves is:

Eyang = a1 b1logt Yang E Yin = a2 b2logt Yin Solve these two linear equations to obtain equilibrium potential formula E = (a2b1-a1b2) / (b1-b2)

The ORP value can be calculated by adding the equilibrium potential to the potential of the reference electrode at this temperature.

Log the data about the two depolarization curves on the computer to automatically calculate the ORP value of the soil.

If this method is used for manual measurement, not only the process operation is tight, the measurement error is large, and the mathematical processing is heavy.

5, ORP depolarization method of automatic measurement equipment

This method is the result of the research by academician Yu Tianren and Professor Liu Zhiguang, electrochemical experts of the Nanjing Institute of Soil Science, Chinese Academy of Sciences. He published many articles in the soil and the British magazine J.SiolSci. in the 1980s. Later, in cooperation with Prof. Fang Jian'an, the PC-1500 pocket computer was developed as an automatic ORP depolarization analyzer (for details, see Fang Jian'an and Liu Zhiguang's Analytical Instruments, 1987, (1), 23.). In the later years, it was developed as a redox depolarization semiautomatic analyzer, FJA-16 redox depolarization automatic analyzer (independent use), and FJA-02 redox depolarization automatic analyzer. (Combined with PC or notebook computer), FJA-3 type redox depolarization automatic analyzer (combined with PC or laptop, high integration), FJA-4 type redox depolarization method automatic Tester (can be used independently, can also be used with a PC or laptop, more integrated).