Acs grade formic acid

HPLC grade methanol was purchased from VWR International (Mississauga, ON, Canada). HPLC grade hexane and ACS grade formic acid and sulfuric acid were purchased from Fisher Scientific (Ottawa, ON, Canada). Water was deionized using a Barnstead water purification system from Fischer Scientific and further filtered through 0.22 μm nylon filters. The high-purity certified reference materials silybin A, silybin B, silychristin, silydianin, isosilybin A, and isosilybin B were purchased from Cerilliant Corporation (Round Rock, TX). A silybin A/B combination standard was provided from Chromadex (Irvine, CA). All standards were stored in a desiccator at −20 °C for long-term storage.