Differential Electrolytic Potentiometry: a Detector in the Flow Injection Analysis of Cyanide Using Silver Electrodes Modified with Carbon Nanotubes

Differential electrolytic potentiometry (DEP) using silver electrodes coated with carbon nanotubes was applied as a detector in a flow injection analysis of cyanide. The direct current differential electrolytic potentiometry (dc-DEP) and the mark-space bias differential electrolytic potentiometry (m.s.b. DEP) both were applied as indicating systems. The parameters that give the best signal were investigated and optimized. A current density of 17μAcm-2 and a percentage bias of 2.8% were found to be optimum in case of dc-DEP and m.s.b. DEP, respectively. The optimum flow rate of both the analyte and the supporting electrolyte was found to be of 85μLs-1 using a coil length of 45 cm. In case of dc-DEP, a linear range of 1–65 ppm of KCN with a detection limit of 0.5 ppm and a relative standard deviation of 2.1% was observed. In case of m.s.b. DEP, a linear range of 1–65 ppm of KCN with a detection limit of 0.35 ppm and a relative standard deviation of 1.5% was observed. The proposed DEP-FIA methods are computer controlled, fast, sensitive, inexpensive and require low consumption of reagents.