Other inactive analogues of vitamin B12 have different lower
ligands, e.g. pseudo-vitamin B12 has adenine as lower ligand.
The
microbiological assay (MBA) does not differentiate between active
forms of vitamin B12 and other corrinoids, thus, an HPLC-MS/MS
method was performed in order to measure the exact molecular
mass of the measured vitamin B12 and distinguish the vitamin
B12 forms.