Analytical HPLC was performed with Lichrosorb silica (Thermo Quest Hypersil, Runcorn, UK) column (15 cm × 4.6 mm i.d.; particle size 5 μm) using two LC-10AT VP pumps. The mobile-phase was n-hexane–acetone–tetrahydrofuran (90:4:6, v/v/v). Before delivering in to the system it was filtered through 0.45 μm, PTFE filter and degassed using vacuum. The analysis was carried out under isocratic conditions using a flow rate of 1.0 ml/min at room temperature (28 °C). Chromatograms were recorded at 475 nm using a SPD-10A VP diode array detector