Determination of berberine and the study of fluorescence quenching mechanism between berberine and enzyme-catalyzed product

A new method for determining berberine has been established based on the principle of fluorescence quenching. The calibration curve was found to be linear between F0/F and the concentration of berberine with the range of 3.00–20.0 μg mL−1. The detection limit was 0.51 μg mL−1 and the relative standard derivative was 0.18%. Effects of pH, foreign ions and the optimization of variables on the determination of berberine have been examined. The mechanism of the fluorescence quenching has been discussed. The binding constant and the number of binding sites were 1.70 × 106 L mol−1 and 1.14, respectively. The data, ΔH = 42.71 kJ mol−1, ΔS = 264.3 J K−1 mol−1 and the mean value ΔG = −39.65 kJ mol−1 were estimated which showed that the reaction was spontaneous and endothermic. The main binding force was hydrophobic force because both ΔH and ΔS were positive.