Development and application of double membrane modified antimony pH electrode and its testing instrument

Abstract: The value of pH is a key chemical parameter in the field of industrial and agricultural production, medicine, environmental protection and other fields. At present, commercial glass pH electrodes have been widely used in soil pH test in the laboratory due to its convenience and reliability. But with turbid and vibrate systems in the filed like on-the-go pH mapping, glass electrode cannot be used because of its brittleness of the glass membrane, sluggish response, which are dif?cult to miniaturize and planarize based on current manufacturing technologies. In this work, a simple, ?exible, inexpensive and effective way to make bilayer membrane modified antimony pH electrode was presented and one pH tester was developed. The surface of the obtained antimony wire was oxidized in sodium dioxide melt to fabricate an antimony oxide ?lm for pH sensing as first layer. The second layer was Nafion membrane with selective characteristics, which was coated after the first layer. The sensing response and open-circuit potential of the electrode had a good linear relationship (R2 =0.997) with pH value in the test solution, which also exhibited small hysteresis, fast response than that of bare antimony pH electrode. The open-circuit potential of the electrode was almost drift-free, with an average variation as small as 0.1mV over an hour. Ion interference experiment showed that this electrode has good selectivity with common ions (Na+, K+, Ca2+, Cl-, Br- ) in soil, redox ion(Fe(CN)63-, Fe(CN)64-) and citrate ions ( C6H5O73- ). The bilayer membrane modified antimony pH electrode and the Ag/AgCl reference electrode as sensor were employed to pH tester, which was designed based on 16 bit low power consumption microcontroller (Sunplus SPCE061A). Tester readings in soil turbid solution under controlled in the lab were compared with the data obtained by standard protocols of soil. The tests demonstrated a high degree of linearity between standard laboratory values and turbid soil solution sensor values, the absolute value of maximum error was less than 0.075, the absolute value of relative error was less than 1.342%. The double membrane modified antimony pH electrode testing instrument would be suitable for in situ and continuous pH measurement in many applications.