Spectrophotometric determination of rosmarinic acid in plant cell cultures by complexation with Fe2+ ions

A spectrophotometric method for determining rosmarinic acid (α-O-caffeoyl-3,4-dihydroxyphenyllactic acid) in unpurified methanolic extracts from Lavandula cell cultures is reported. It is based on a complexation reaction of rosmarinic acid with Fe²⁺ to give a blue-dark product with λ_max=572 nm and ?₅₇₃=3.82×10³ l mol^?1 cm^?1. The stoichiometry of the reaction and the optimal conditions for colour development are checked. The sensitivity and accuracy of this spectrophotometric method are compared with UV-spectral and HPLC methods for determining rosmarinic acid in plant cell cultures; similar results are obtained.