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

The reversible redox couples (Fe(III)/Fe(II); Ce(IV)/Ce(III); Fe(CN)(6)(3-) /Fe(CN)(6)(4-); I-2/I-; Br-2/Br- and VO3-/VO2+) were studied as indicating redox systems for biamperometric determination of paracetamol in a flow inj ection assembly. Considering the selectivity of assayed systems against exc ipients and antioxidants that typically are presented in pharmaceutical for mulations (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 oxi dant stream where the drug was oxidised by excess oxidant. The observed sig nal (current): showed a linear dependence on the concentration of reduced s pecies. The calibration graphs were linear over the range 0.1-7 mu g ml(-1) of paracetamol for iron(III) and up to 20 mu g ml(-1) for metavanadate, wi th a relative standard deviation of 1.6 and 1.5% (5 mu g ml(-1) paracetamol ; n = 20) and a sample throughput of 149 and 79 h(-1) for iron(III) and met avanadate, respectively. Under flow optimal chemical and conditions for det ermining paracetamol both indicating systems were tested for different fami lies compounds of pharmaceutical interest (phenothiazines, sulphonamides, n itrocompounds, epinephrine derivates, tetracyclines and pyridine derivates) . (C)1999 Elsevier Science B.V. All rights reserved.