Traceable quantitation of cyanocobalamin (vitamin B12) via measurement of cobalt and phosphorus: a comparative assessment using inductively coupled plasma atomic emission spectrometry (ICP-AES) and ion chromatography (IC)

Traceable and precise quantitative measurements of cyanocobalamin (CN-Cbl) have been hampered by the lack of well characterized standards and pure materials of this bio-inorganic analyte that belongs to the water-soluble vitamins of the B-group known as vitamin B-12. Measurement of cobalt and/or phosphorus content of vitamin B-12 offer an approach for its quantitation that is traceable to the International System of Units (SI) with low measurement uncertainty. Cobalt and phosphorus measurements of CN-Cbl were carried out by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and Ion Chromatography (IC). Use of a mixed bed ion exchange column coupled with post column reaction, IC provides a means to differentiate free cobalt from the cobalt complexed inside the corrin ring of the CN-Cbl molecule. In the case of ICP-AES and IC, a prerequisite for quality measurement is the purity of the starting vitamin B-12 material. The relative expanded uncertainties (% U) expressed at 95% confidence for these analyses range from 0.3 to 1%.