Development of an analytical method to quantify total isoflavones in phytotherapic capsules using high-performance liquid chromatography

Isoflavones can be found in grains and leaves of soybean. Currently, these are sold in pharmacies as phytotherapic capsules. Isoflavones have been recommended by doctors, especially for women, due to their ability to relieve menopause symptoms, among other benefits. However, no method exists for the official control of isoflavone content in capsules sold in the Brazilian market. This study aims to develop an appropriate analytical method to determine the total isoflavone content (daidzin, glycitin, and genistin, and their respective aglycone forms) in phytotherapic capsules purchased in pharmacies in Curitiba, Parana State, Brazil, using the technique of high-performance liquid chromatography with UV detection (UV-HPLC). The HPLC system consisted of a quaternary pump, an autosampler, and Waters reversed-phase C-18 column (5 mu m x 300 mm. Analyses were carried out at 40 degrees C, using a flow rate of 1.0 mL/min (acetonitrile and acetic acid 0.1%), and detection was performed at 254 nm. The method was validated as required by ANVISA and showed to be reliable for the following parameters: linearity (r(2) > 0.99), selectivity (correlation between 0.99 and 1.00), precision (relative standard derivation < 1.59%), accuracy (from 80% to 111.63% intraday and from 80% to 117.88% interday recovery), and robustness.