The Eagle Biosciences Vitamin B12 quantitative test is based on the principle of the enzyme linked immuno sorbent assay. An antibody directed against vitamin B12 is bound on the surface of a microtiter plate. Vitamin B12 containing samples or standards and a vitamin B12-peroxidase conjugate are given into the wells of the microtiter plate. Enzyme labelled and free vitamin B12 compete for the antibody binding sites. After one hour incubation at room temperature, the wells are washed with diluted washing solution to remove un bound material. A substrate solution is added and incubated for 20 minutes, resulting in the develop ment of a blue colour. The colour development is inhibited by the addition of a stop solution, and the colour turns yellow. The yellow colour is measured photometrically at 450 nm. The concentration of vi tamin B12 is indirectly proportional to the colour inten sity of the test sample. Sample Types: food products. Range: 0.4 - 40 ng/ml. Sensitivity: 0.3 ng/ml. Time: 1.5 hours ? Vitamin B12 as a trace element belongs to the biologi cally important chelate formers. The basic unit con sists of a corrin ring with cobalt as a central atom. Cobalt is six fold coordinated by four nitrogen atoms, one cyanide and a dimethylbenzimidazol group. Vi tamin B12 forms a stable complex, which is absorbed in the lower part of the small intestine, with the so-called intrinsic factor present in the gastric juice. A lack of vitamin B12 can lead among other things to pernicious anemia. This disease is not generated by an insufficient supply of vitamin B12, but by the ab sence of intrinsic factor. A pernicious anemia can be treated by a high dosage of vitamin B12.