Generation and destruction of unstable reagent in flow injection system: determination of acetylcysteine in pharmaceutical formulations using bromine as reagent

A flow injection spectrophotometric procedure was developed for determination of acetylcysteine in sachets and liquid formulations. The determination of this drug was carried out by reacting it with bromine chemically generated in flow injection system monitored continuously at 400 nm. Acetylcysteine reacts with bromine causing a decrease in the absorbance that is proportional to the analyte concentration. The bromine in excess was destroyed on-line by an ascorbic acid solution before the discard. The calibration curve for acetylcysteine determination was linear in the concentration range from 1.6 × 10−4 to 1.6 × 10−3 mol/l with a detection limit of 8.0 × 10−5 mol/l. The relative standard deviation (R.S.D.) was lesser than 1.2% for a solution containing 5.3 × 10−4 mol/l acetylcysteine (n = 10), and 60 determinations per hour were obtained.