Cyanocobalamin is the most common and widely-produced of the vitamin B12 analogs. Vitamin B12, important for proper neuronal function and formation of blood cellular components, is monitored directly in patient serum samples by LC-MS/MS. This certified solution standard is suitable for use as a starting material in the preparation of linearity standards, calibrators or controls in a variety of testing applications from diagnostic testing of vitamin B12 deficiency by LC-MS/MS to quality control testing of vitamin B12-based dietary supplements/fortified foods or pharmaceutical preparations.