Direct spectrophotometric determination of quercetin in the presence of ascorbic acid

The current research provides a simplified sample preparation procedure for the accurate estimation of quercetin in pure and in the pharmaceutical dosage form. Direct spectrophotometric method for the determination of quercetin in the presence of ascorbic acid was established. The influences of medium, wavelength, pH, temperature and the ionic strengths on quercetin determination were investigated. The best conditions for calibration curve are: 50% ethanol, lambda = 370 nm, pH = 4.2, T = 34 degrees C and I = 7.5 x 10(-5) M. Beer's law is obeyed in the concentration range 1.0-12.0 microg ml(-1) for quercetin. The corresponding detection limit is 0.76 microg ml(-1). The proposed method was verified by analyzing Quercetin + C capsules, Twinlab.