Validated method for the quantitation of quercetin from human plasma usinghigh-performance liquid chromatography with electrochemical detection

A validated method for the quantitation of trace levels of quercetin from h uman plasma to be used in pharmacokinetic and biomarker studies is presente d. Quercetin conjugates were hydrolysed enzymatically, plasma proteins were removed using a Bond Elut C18 extraction column and additional interferenc es were removed by extracting them into a toluene-dichloromethane mixture. The HPLC system consisted of an Inertsil ODS-3 column (250x4.0 mm) and a mo bile phase with 59% methanol in phosphate buffer (pH 2.4). High selectivity and a low quantitation limit (0.63 mu g/l) were achieved by using electroc hemical detection at a low potential. The method has excellent reproducibil ity: R.S.D. values of peak-heights were 2% and 7.9%, respectively, for with in-day and between-day precision. The method was applied to a small scale s tudy of quercetin pharmacokinetics and quercetin was shown to be absorbed f rom a 20 mg dose. No free quercetin was detected in plasma and no evidence of significant amounts of quercetin glycosides in plasma was found. (C) 199 9 Elsevier Science B.V. All rights reserved.