A Certified Spiking Solution® of D6-25-Hydroxyvitamin D3 (26,26,26,27,27,27-D6) in ethanol at a concentration of 50 mg/mL. This new internal standard is suitable for critical quantitative applications in research and clinical environments including for use in preparation of calibrators for LC/UV and LC-MS/MS assays and isotope dilution methods. The stable, quantitative solution format provides significant benefits to the user including material savings, increased efficiency of labor, and convenience of use. The shelf stable Snap-N-Spike® format allows laboratories to eliminate painstaking weighing operations and provides the ability to spike a known concentration of analyte into their matrix of choice just before use.