Development of a selective HPLC-DAD/ELSD method for the qualitative and quantitative assessment of commercially available Eurycoma longifolia products and plant extracts.

Aqueous extracts of the roots of Eurycoma longifolia are traditionally used to improve sexual performance, to treat infertility and other sexual dysfunctions but also to increase muscle strength. Nowadays, many different products are commercially available which are promoted as E. longifolia extracts and claim to possess beneficial aphrodisiac effects. Since such herbal aphrodisiac preparations have been recently the target of fraudulent product counterfeiting and because eurycomanone, one of the main quassinoids of E. longifolia, is suspected to possess toxic effects at higher concentrations, a highly selective HPLC-DAD/ELSD method has been established to analyze commercially available products and extracts of plant material. The presented method was established by the use of a mixture of 27 reference compounds for qualitative issues and fully validated according to the ICH guidelines for the quantification of three quassinoides: laurycolactone A, longilactone, and eurycomanone. The calibration curves of these showed a linearity over a range of 0.05 to 1.0mg/ml, with a regression coefficient not lower than R=0.9969. The inter-day and intra-day precision (indicated as relative standard deviation) of the developed method was <2.9%. The recovery ranged from -3.3% to +6.0%. Eight randomly purchased products have been analyzed with this method, but only five of them contained E. longifolia compounds in detectable amounts. The concentration of eurycomanone in these products varied from 0.22±0.002mg eurycomanone per capsule to 1.84±0.08mg corresponding to a maximal recommended daily intake of 0.76±0.02 to 31.90±0.21mg.