Quantitative Analysis of Isoflavones and Caffeine

Formononetin, biochanin A, daidzein, genistein, caffeine, [trimethyl-¹³C₃]-caffeine, tolbutamide, dextromethorphan, [methyl-d₃]-dextromethorphan, alprazolam, [phenyl-d₅]-alprazolam, and Helix pomatia β-glucuronidase and arylsulfatase were purchased from Sigma-Aldrich (St. Louis, MO). [butyl-d₉]-4-Hydroxy-tolbutamide was purchased from Toronto Research Chemicals (Toronto, Canada). LC-MS grade acetonitrile and methanol were purchased from VWR (Radnor, PA), and LC-MS grade formic acid was purchased from Thermo Scientific (Rockford, IL). Water was prepared using an Elga Purelab Ultra (Siemens Water Technologies, Woodridge, IL) water purification system. Blank serum obtained from individual donors was purchased from BioIVT (Westbury, NY). The red clover dietary supplement was standardized chemically and biologically^{32 (link)} and had been used in our previous clinical trials.^{33 (link),34 (link)}