A rapid and precise assay for peroxide as ‘active oxygen’ in products, by flow injection analysis in a high pressure system with spectrophotometric detection

A simple, rapid and automated assay for ‘active oxygen’ originating from hydrogen peroxide, or other organic peroxides, in products is presented employing flow injection (FI) analysis. The product is dispersed and peroxide dissolved in a solvent of 5% (v/v) acetic acid, which constitutes the carrier stream. Ammonium molybdate can be added to this carrier stream to increase sensitivity as required. The sample solution is injected into the acid carrier stream, which is then merged with iodide ion in situ in a two-stream manifold. The ‘active oxygen’ in the product oxidises acidified iodide to iodine, which is detected spectrophotometrically at 350 nm. The closed conditions prevent interference from atmospheric oxygen and the short reaction time minimises the potential for interference from side reactions. Standard HPLC equipment is used throughout, employing a back-pressure to improve precision (high pressure flow injection). Conditions have been investigated using screening multivariate experimental design (two-level quarter fractional factorial design incorporating centre points) to identify and optimise the critical variables. The method has been fully validated (with sample solution R.S.D.s typically < 0.5%, LOQs of 0.04 or 0.006 μg ml−1 as ‘active oxygen’ for acid or acid/molybdate carriers respectively) and is quicker and simpler than the currently employed manual titration approach. It should be applicable to a range of ‘active oxygen’ products.