Isocratic LC-DAD-FLD method for the determination of flavonoids in paprika samples by using a rapid resolution column and post-column pH change.

The determination of flavonoid compounds in paprika samples has been performed by liquid chromatography in series diode array and fluorescence detection (LC-DAD-FLD), by means of a pH change to basic medium just before FLD detection. The validation of the method was performed through the establishment of the external standard calibration curves and the analytical figures of merit. Limits of detection ranging from 0.006 to 0.02 mg L(-1) and 0.007 to 0.09 mg L(-1) were achieved using DAD and FLD detection, respectively. The experimental conditions to carry out the hydrolysis procedure to obtain flavonoid aglycones from flavonoid glycosides have been optimized applying an experimental design and the response surface methodology. The final conditions selected were 2.5M HCl during 45 min at 85°C. The repeatability of this procedure was assayed and relative standard deviation (RSD) values for concentration of quercetin and luteolin compounds were lower than 2%. The quantification of quercetin, luteolin and kaempferol compounds was carried out in less than 6 min in paprika samples by means of the external standard calibration. The analytes were extracted with methanol and the extracts were previously subjected to a cleanup procedure to extend the use of the chromatographic column.