Polycarbonate culture bottles, PTFE tubing, and silicone tubing were soaked in 1% detergent (Citranox) for one week, rinsed with deionized water, soaked in 10% HCl (Trace Metal Grade, Fisher Scientific) for another week, then rinsed with ultrapure water (qH2O, 18 MW cm -1 ) before use. Solid phase extraction columns (1 g, 6 mL Bond Elut ENV, Agilent) were activated by passing 6 mL of methanol (MeOH) through the resin, rinsed with 6 mL of pH 2 qH2O followed by 6 mL of qH2O. A 1 µM aqueous cyanocobalamin (Sigma Aldrich) solution was used as an internal standard. For analyses coupling liquid chromatography (LC) with inductively coupled plasma MS (ICP MS), LC-MS grade methanol, ammonium formate (Optima, Fisher Scientific), and qH2O were used. The methanol was redistilled using a polytetrafluoroethlene (PTFE) still to reduce metal contaminants. For LC-FT-ICR MS analyses, LC-MS grade water, methanol, and ammonium formate (Honeywell) were used.