No abstract

Paracetamol is an extensive analgesic and antipyretic drug. Several batch methods have been reported for the determination of paracetamol in pharmaceutical preparations, such as spectrophotometry, 1-6 reflectance near-infrared spectroscopy, 7 chemiluminescence 8 and liquid chromatography. 2 A number of flow-injection (FI) methods have also been reported for the determination of paracetamol, such as FI-spectrophotometry, using different on-line derivatization reactions. However, the control of such reactions and/or manifolds is still complicated. 9-12 Some methods, such as FI-FTIR 13 and FI with a boron-doped diamond thin film electrode, 14 involve relatively higher cost instruments.A further generation of FIA, SIA is a great potential technique for chemical analysis due to much less reagent consumption, its simplicity and convenience with which manipulation can be automated.So far, an SI procedure for paracetamol determination has been reported. It is based on a reaction with hexacyanoferrate(III), followed by a reaction with phenol at elevated temperature in aqueous ammonia. 15 Simple and inexpensive spectrophotometric flow-injection and sequential-injection systems for the determination of paracetamol using simple reagents based on preliminary concepts introduced at the ICFIA 2001 Conference, 16 are presented. The procedures employ the reaction of paracetamol with nitrous acid at room temperature, producing a derivative. Experimental Chemicals and reagentsAll of the reagents used were of analytical reagent grade. Deionized water was used throughout the experiments. A stock solution (5000 mg/l) of 4-acetaminophenol standard (paracetamol, Fluka, Switzerland), which was assayed using the USP method, 18 was prepared by dissolving 0.5146 g of the standard in water and diluting to the mark in a 100 ml volumetric flask. Working standards were freshly prepared by diluting the stock solution with water to obtain appropriate concentrations. Sample preparationSome locally commercial pharmaceutical preparations were taken as samples to be assayed. For tablet samples, 20 tablets were accurately weighed and finely powdered. An amount of the powder equivalent to a tablet was dissolved in water. After stirring for 15 min at a temperature of 60 -70˚C, the volume was made to 250 ml. The solution was then filtered before analysis. Further appropriate dilutions for FIA procedures were made using water.For a syrup sample, an aliquot corresponding to 200 mg of paracetamol was diluted to 100 ml