The spectrophotometric determination of hydroperoxide and peroxide in a lipid pharmaceutical product by flow injection analysis

A sensitive, rapid and automatable flow injection analysis procedure is described for the determination of total hydroperoxides and peroxides in lipid products. All unsaturated lipids are susceptible to degradation by oxidation, and the quantification of these major oxidation products is an essential measure of lipid product stability. In this methodology a lipid emulsion is dispersed and injected into an acidic solution of propan-2-ol, which is then merged with iodide ion in situ in a two-stream manifold. The lipid hydroperoxide 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 interference from side reactions. Conditions were optimised, using experimental design, for a lipid product under development at GlaxoWellcome. A two-level half-fractional factorial design was applied to screen for the critical factors, followed by a multi-level central composite design to optimise these variables. The resulting method was fully validated and is linear down to 0.1 nmol ml-1. This approach should be applicable to other lipid formulations and offers significant advantages in terms of speed, automation and precision compared with existing manual procedures.