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 urin e samples were extracted with diethyl ether, or pre-digested with sulfatase and/or beta-glucuronidase followed by extraction. The isoflavones were sep arated using gradient LC methods and detected by negative single ion monito ring on an MS system using a heated nebulizer atmospheric pressure chemical ionization interface. CVs for inter- and intra-assay variability were gene rally <20 and 10%, respectively. Preliminary studies using these procedures demonstrate 52+/-4 and 26+/-4% of genistein in rat urine was found as the aglycone and sulfate conjugates, respectively, compared to 0.36 and 4%, res pectively, in human urine. This method is suitable for the study of isoflav one sulfate conjugates in biological fluids. (C) 1999 Elsevier Science BN. All rights reserved.