Study of various indicating redox systems on the indirect flow-injection biamperometric determination of pharmaceuticals Original Research Article

The reversible redox couples (Fe(III)/Fe(II); Ce(IV)/Ce(III); Fe(CN)63–/Fe(CN)64−; I2/I−; Br2/Br− and VO3−/VO2+) were studied as indicating redox systems for biamperometric determination of paracetamol in a flow injection assembly. Considering the selectivity of assayed systems against excipients and antioxidants that typically are presented in pharmaceutical formulations (e.g. sucrose, glucose, ascorbic acid and hydrogen sulphite) the systems Fe(III)/Fe(II) and VO3−/VO2+were selected for the determination of the drug. The sample was injected into a carrier which merged with the oxidant stream where the drug was oxidised by excess oxidant. The observed signal (current) showed a linear dependence on the concentration of reduced species. The calibration graphs were linear over the range 0.1–7 μg ml−1 of paracetamol for iron(III) and up to 20 μg ml−1 for metavanadate, with a relative standard deviation of 1.6 and 1.5% (5 μg ml−1 paracetamol; n = 20) and a sample throughput of 149 and 79 h−1 for iron(III) and metavanadate, respectively. Under flow optimal chemical and conditions for determining paracetamol both indicating systems were tested for different families compounds of pharmaceutical interest (phenothiazines, sulphonamides, nitrocompounds, epinephrine derivates, tetracyclines and pyridine derivates).