Dual-stream flow injection method for amplified electrochemical detection of ferrocene derivatives

A dual-stream flow injection method has been developed for electrochemical detection of ferrocene derivatives in flow streams. The method is based on a previously described electrochemical amplification method in which currents for analyte oxidation are enhanced by rapid analyte regeneration via a solution-phase electron exchange reaction with a sacrificial reagent. The use of two independent flow channels in the present method, one to carry the analyte and another to supply the sacrificial reagent, eliminates the necessity of spiking samples and calibration standards with sacrificial reagent to avoid injection transients. Hydrodynamic voltammograms were recorded for a series of injections of hydroxymethylferrocene (HMFc, a model ferrocene analyte) into the carrier stream in the presence and absence of ferrocyanide (which serves as sacrificial reagent) in the reagent stream. From these voltammograms an optimum detection potential for HMFc of +0.8V versus Ag|AgCl|KClsat was selected. Two different concentrations of sacrificial reagent were tested for a range of HMFc concentrations between 1×10^-3 and 1×10^-8M for which both unamplified and amplified peaks could be detected. An amplification factor of approximately 300 was obtained for a 1×10^-8M HMFc injection with 2×10^-4M ferrocyanide present in the reagent stream.