Digital-image photometry and salting-out assisted liquid-liquid microextraction for determination of flavonols in berries

The metal-chelating ability of flavonols is exploited in spectrophotometric screening methods, but the content is often overestimated due to interferences by anthocyanins and phenolic acids. In order to circumvent this drawback, liquid-liquid microextraction with acetonitrile is proposed for the separation of flavonols from anthocyanins and further partitioning to the aqueous phase as Al(III) complexes with the working pH adjusted to 3.5 to avoid the interference of phenolic acids. The standard addition method circumvented the matrix effects in photometric measurements by digital-image photometry. A linear response was achieved up to 10 mg L-1 quercetin, with coefficient of variation (n = 10) and limits of detection and quantification estimated at 3.1%, 0.5 and 1.7 mg L-1, respectively. Accurate results were achieved in comparison to the spectrophotometric reference procedure. The proposed procedure is a simple and cost-effective approach, with low reagent and solvent consumption (105 & mu;g of Al(III), 15 mg of NaCl, and 1.2 mL of acetonitrile) and waste generation (1.5 mL) per determination.