Materials.

Four beer samples were used as representative of diverse complex mixtures (SI Appendix, section S3). Ten milliliters of beer were sampled directly after opening and stored at −20°C before extraction. After thawing, (i) 200μL of beer was mixed with 600μL of methanol/chloroform, (ii) sonicated for 5 min at room temperature; (iii) and centrifuged for 5 min (12,000  ×  g) at room temperature. The supernatants were stored at −80°C. Urine fragmentation data from an earlier approved and published study on metabolite annotation of urinary metabolites were used for validation purposes (16). HPLC-grade methanol, acetonitrile, and analytical reagent-grade chloroform were acquired from Fisher Scientific. HPLC-grade H₂O was purchased from VWR Chemicals. Formic acid (for MS) and ammonium carbonate were acquired from Fluka Analytical (Sigma-Aldrich).