Simultaneous Determination of Isoflavones and Equol in Egg Yolk Using UPLC-MS/MS

Abstract

A simple and reliable analytical method based on ultra-high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) was developed and validated for the simultaneous determination of total isoflavone aglycones and its metabolite equol in egg yolk. The seven target analytes were separated on an Acquity ultra performance liquid chromatography (UPLC) system BEH C18 column with gradient elution and detected by electrospray ionization source (ESI) operating in negative subsection acquisition mode under multiple reaction monitoring (MRM) conditions. The results showed that the recoveries of spiked isoflavones and equol from the matrices were satisfactory, ranging between 73.74 and 89.35%, and all with relative standard deviation (RSD) values below 10%. The linearity of their corresponding concentration ranges from 2 to 500 ng/mL with correlation coefficients (r2) all higher than 0.99. The analytes were stable under the experimental conditions and the proposed method exhibited good recovery and reproducibility within only 8 min. The measurement results showed that the tested eggs contained soy isoflavones and equol, which may be beneficial for people who lack estrogens and those with hormone-related disorders. This method can also be useful for the determination of isoflavones and equol in other animal products.