Quantitative determination of diterpene acids in garden sage leaves

A procedure is developed for the quantitative determination of diterpene acids in garden sage leaves by UV spectrophotometry at the wavelength 285 nm. The target group of compounds was selectively extracted by petroleum ether 40/70. It was shown that the completeness of extraction is determined mainly by the number of portions of the pure solvent: at the optimum ratio of the mass of the weighed portion to the volume of solvent 1 g/200 mL, double extraction is sufficient. The duration of each extraction is 20 min. The procedure was used in the analysis of samples of garden sage leaves from various producers. It was found that the concentration of diterpene acids in samples varied from 2.1 to 3.6 wt % (in terms of carnosic acid). The error of a single determination of the sum of diterpene acids in garden sage leaves is ±2.38% (P = 0.95).