Simple spectrophotometric assessment of the trans-/cis-resveratrol ratio in aqueous solutions

The solubility and molar absorptivity of trans- and cis-resveratrol isomers in aqueous solvents are poorly described. This study aimed to develop and describe a new simple method for the determination of trans- and cis-resveratrol concentrations in aqueous solutions. Up to 300 μM trans-resveratrol was dissolved in water by sonication for 2 h. Cis-resveratrol was obtained by exposing a 100-μM trans-resveratrol aqueous solution to sunlight for 8 h, followed by HPLC separation and analysis by mass spectrometry (resveratrol oxidation products were absent). Accurate values for UV absorbance in water were ελmax=ε304 nm=30 335 M−1 cm−1ελmax=ε304 nm=30 335 M−1 cm−1, ɛ286 nm = 23 400 M−1 cm−1 for trans-resveratrol and ελmax=ε286 nm=14 986 M−1 cm−1ελmax=ε286 nm=14 986 M−1 cm−1, ɛ304 nm = 9515 M−1 cm−1 for cis-resveratrol. These values allowed us to propose formulae to assess the trans-/cis-resveratrol ratio in water, using a simple and reliable UV–vis spectrophotometric method. Statistical analysis revealed no significant difference between our UV method and the commonly used HPLC method. All these data are transferable to 150 mM NaCl and 10 mM phosphate buffer solutions, which could be particularly useful for cell culture, ex vivo and in vivo studies.