Cobalamin Assay by the Radioisotope Tracer Method : A Collaborative Study Report of the U.S.P.-N.F. Joint Panel

Four commercial type samples were examined by a radioisotope tracer method by nine collaborators. The samples studied were cobalamin concentrates and liver extracts, but subsequent reports from several collaborators show the method to be applicable to vitamin B12 intrinsic Factor concentrate samples. Satisfactory results were submitted by all collaborators. A statistical study of the results shows that the method is specific for cobalamins; red pigments occurring in the manufacture of cobalamins and which might occur in commercial products do not interfere in the method. The accuracy of the method judged by comparison with a reference sample of cyanocobalamin is satisfactory. The results were in good agreement with those of the U. S. P. microbiological method for those samples that did not contain "red pigments." A standardization of the tracer solution is given in the method which provides a correction factor for the purity of the radioactive tracer used and also forms a basis for comparing all results obtained by the method with that of a reference standard of cyanocobalamin.