Comparison of analytical methods for the quality control of a new formulation containing soy extract and melatonin

Soymen GN is a new commercial preparation, containing soy extract and melatonin for the treatment of menopausal symptoms such as insomnia, hot flushes, tachycardia and osteoporosis. The commercial package contains two kinds of soft gelatin capsules: the “light” capsules for morning administration contain soybean extract (40 mg), while the “dark” capsules for evening administration contain soy extract (40 mg) and melatonin (5 mg). The main active compounds are the isoflavones, which are present both as aglycones and as glycosides: genistein, daidzein, glycitein, genistin and daidzin. These compounds are of particular interest for their possible estrogenic effects on the symptoms of menopause, in fact they have been used in therapy as a replacement to estrogen deficiency as a consequence of menopause. Melatonin is a hormone whose main function is the regulation of circadian rhythms. Thus, it can be helpful for the relief of insomnia and other sleep disturbances. The aim of this study is to develop a quality control system for the Soymen GN formulation. For this purpose, it is important to have access to reliable analytical methods for the determination of melatonin and of the main soy isoflavones, both aglycones and glycosides. Two original HPLC methods coupled to spectrophotometric and amperometric detection, respectively, have been developed for the quality control of Soymen GN capsules. UV detection is carried out at 260 nm, while amperometric detection is carried out at an oxidation potential of + 800 mV. The chromatographic separation is obtained using a reversed-phase C8 column as the stationary phase and a mixture of acetonitrile and an acidic phosphate buffer (30/70, v/v) as the mobile phase. A third analytical method based on micellar electrokinetic chromatography is currently undergoing validation. The BGE is composed of a 25 mM, pH 10.3 carbonate buffer, containing 55 mM SDS and 5% methanol. The analytes are quantitatively extracted from both “light” and “dark” capsules by agitation in a methanol/water mixture. From these preliminary results, all three methods seem to be promising for the quality control of the new formulation.