An LC–MS method to determine concentrations of isoflavones and their sulfate and glucuronide conjugates in urine

Most methods for detecting isoflavones in biological samples do not measure the concentration of sulfate conjugates. An LC–MS method is reported here to estimate urinary concentrations of genistein and daidzein, their sulfate and glucuronide conjugates and other major metabolites. Human and rat urine samples were extracted with diethyl ether, or pre-digested with sulfatase and/or β-glucuronidase followed by extraction. The isoflavones were separated using gradient LC methods and detected by negative single ion monitoring on an MS system using a heated nebulizer atmospheric pressure chemical ionization interface. CVs for inter- and intra-assay variability were generally