Comparative Evaluation of Four Methods for Assay ofcis-andtrans-Resveratrol

Abstract

A comparative evaluation of four methods to measure the concentrations of <i>cis-</i> and <i>trans-</i>resveratrol as well as total resveratrol in commercial wines has been performed. Two of these methods utilized solid-phase extraction of resveratrol isomers prior to analysis by direct-injection gas-chromatography mass-spectrometry (GC-MS) or derivatization with <i>bis</i>-[trimethylsilyl]-trifluoroacetamide (BSTFA) prior to GC-MS analysis. Two methods utilized direct-injection high performance liquid chromatography (HPLC) in normal phase (isocratic) with absorbance detection at 306 nm, and reverse phase HPLC with gradient elution and diode array detection. In virtually all comparisons, the correlation between the values for any two methods was very satisfactory (r &gt; 0.900), but some evidence of systematic bias was obtained which could not be explained by different standardization techniques. High values for <i>trans-</i>resveratrol with direct-injection GC-MS (Method 1) could be attributed, at least in part, to thermal breakdown of resveratrol glucosides to free isomers. The derivatization GC-MS technique (Method 2) showed a tendency to overestimate <i>cis-</i>resveratrol and underes- timate the trans isomer, possibly as a consequence of <i>trans-</i> to-<i>cis</i> isomerization during the derivatization step. Somewhat lower values for <i>cis-</i>resveratrol with the normal-phase HPLC procedure (Method 3) might be a consequence of monitoring a single wavelength (306 nm) which is well above the absorption maximum of this isomer. Method 4 (reverse-phase gradient HPLC with diode array detection) has the advantage of allowing the simultaneous quantitation of many other polyphenols of biologic interest, and as of now may be considered to be the most robust method for routine application.