Optimization of solid-phase extraction of non-coloured phenolic compounds from fortified wines using response surface methodology

Non-coloured phenolic compounds were determined by high performance liquid chromatography in samples of fortified wines. A solid-phase extraction procedure was optimized for pretreatment of the sample, whose optimization used surface response methodology. The variables evaluated were sample volume, elution solvent volume and flow rate. Application of the surface response methodology revealed that the conditions for extraction were 5 mL of sample, 20 mL of elution solvent and flow rate 0.06 mL s(-1). Verification tests gave percent recoveries in the interval between 71.06 and 119.40%. The optimized method was applied to samples of white and red fortified wines with good results for determination of gallic acid, (+) catechin, caffeic acid, p-coumaric acid, ferulic acid and quercetin, indicating the suitability of the model employed and the applicability of surface response methodology in optimization of the extraction conditions.