25-hydroxyvitamin D3, D6-25-hydroxyvitamin D3, and 3-epi-25-hydroxyvitamin D3 standards (100 μg/mL in ethanol) were purchased from IsoSciences (King of Prussia, PA). These standards were diluted to a final concentration of 10 μg/mL in Fisher Optima LC-MS grade water, purchased from Fisher Scientific (Pittsburgh, PA), with no additives.
Lithium acetate, magnesium acetate tetrahydrate, and calcium acetate monohydrate were purchased from Acros Organics (Geel, Belgium). Potassium acetate was purchased from Alfa Aesar (Haverhill, MA). Rubidium acetate was purchased from Strem Chemicals (Newburyport, MA). Cesium acetate was purchased from MP Biomedicals (Santa Ana, CA). Strontium acetate was purchased from Sigma-Aldrich (St. Louis, MO). Barium acetate was purchased from Chem-Impex International, Inc. (Wood Dale, IL). These standards were combined with the aforementioned vitamin D standards and were diluted to a final concentration of 10 μg/mL in Fisher Optima LC-MS grade methanol or a 1:1 mixture of Fisher Optima LC-MS grade water and methanol, depending on their relative solubility. Flame emission testing was used to estimate the sodium concentration in the solvents as approximately 185 ppb (water) and 220 ppb (methanol).
Lithium acetate, magnesium acetate tetrahydrate, and calcium acetate monohydrate were purchased from Acros Organics (Geel, Belgium). Potassium acetate was purchased from Alfa Aesar (Haverhill, MA). Rubidium acetate was purchased from Strem Chemicals (Newburyport, MA). Cesium acetate was purchased from MP Biomedicals (Santa Ana, CA). Strontium acetate was purchased from Sigma-Aldrich (St. Louis, MO). Barium acetate was purchased from Chem-Impex International, Inc. (Wood Dale, IL). These standards were combined with the aforementioned vitamin D standards and were diluted to a final concentration of 10 μg/mL in Fisher Optima LC-MS grade methanol or a 1:1 mixture of Fisher Optima LC-MS grade water and methanol, depending on their relative solubility. Flame emission testing was used to estimate the sodium concentration in the solvents as approximately 185 ppb (water) and 220 ppb (methanol).