Solid-phase extraction procedure for determination of phenolic acids and some flavonols in honey

The solid-phase extraction procedure (SPE) for isolation and preconcentration of phenolic acids (gallic, p-HBA, p-coumaric, vanillic, caffeic and syringic acid) and some flavonols (rutin, quercetin and kaempferol) from honey samples prior to their determination by HPLC is reported. Different solid sorbents such as Bond Elut octadecyl C18, Oasis HLB, Strata-X and Amberlite XAD-2 were tested for this purpose. The best results were obtain when aqueous solution of honey (100 mL) was adjusted to pH 2 and passed through the microcolumn containing 2.5 g of Oasis HB followed by washing the sorbent with 50 mL of acidified water (pH 2). The analytes were then eluted with methanol. The proposed method permits the quantification of the studied compounds with the limit of detections ranged from 25 ng kg−1 to 0.75 μg kg−1 for p-HBA and quercetin, respectively. The precision of the overall analytical procedure was estimated by measuring the within-day repeatability and the relative standard deviations of the parallel (n = 3) results were in the range of 1.9–10.1%. The method was tested for real honey samples from different botanical origins.