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, λ = 370 nm, pH = 4.2, T = 34°C and I = 7.5 × 10-5 M. Beer's law is obeyed in the concentration range 1.0-12.0 μg ml-1 for quercetin. The corresponding detection limit is 0.76 μg ml-1. The proposed method was verified by analyzing Quercetin + C capsules, Twinlab®

Effects of flavonoids on plasma coagulation tested in vitro by "screening tests"

The effects of four flavonoids: rutin, quercetin, morin and hesperidin on plasma coagulation has been examined by measuring aPTT, TT and PT. It is found that water solution of these flavonoids shows no effects in the measured quantities. This is due to their low solubility in water, and therefore, their low concentrations. Ethanolic solutions of these studied flavonoids, however, show significant prolongation of all measured coagulation times, but compared to ethanol alone, their anticoagulant effects are smaller. It is suggested that the observed effects can be attributed to the interaction of flavonoids with human plasma proteins

Spectrophotometric investigation of the Pd(II)-quercetin complex in 50% ethanol

Composition and stability constant of the Pd(II)-quercetin complex were determined by suitable spectrophotometric methods and pH-metric measurements in 50% Ethanol. It was found that the pd(2+) ion and quercetin form a 1:1 complex in which Pd2+ is linked to quercetin through the carbonyl and the 3-hydroxyl group. The stability constant log beta(1) ranged from 6.05 at pH = 5.00 to 4.96 at pH = 6.50. The conditions for the spectrophotometric determination of quercetin by means of complex formation were investigated. Beer's law was obeyed up to 5.00 x 10(-5) M quercetin