Quantitative analysis of forskolin in Coleus forskohlii (Lamiaceae) by reversed-phase liquid chromatography

A rapid method was developed for the evaluation of forskolin in Coleus forskohlii Briq. (Lamiaceae). Forskolin was quantitated in the root and stem of dried C. forskohlii and in 17 market products by reversed-phase liquid chromatography (LC) with a photodiode array detector at 210 nm. The temperature was held constant at 30 degrees C, and the retention time of forskolin was approximately 6.8 min. The samples were extracted with acetonitrile by sonication. The precision of the method was confirmed by a standard deviation < 5.0% (n = 3), and forskolin recovery was 99.1%. Limit of detection was 1.5 microg/mL, and the response was linear through zero from 6.3 to 630 microg/mL with a correlation coefficient (R2) of 0.9998. Identity of the marker compound was confirmed by an LC/mass spectrometry experiment. The method was successful in the qualitative and quantitative evaluation of the marker compound in C. forskohlii plant material and in market products claiming to contain C. forskohlii.