Radioactive Tracer Assay for Vitamin B₁₂ and Other Cobalamins in Complex Mixtures

Cobalamin Assay by the Radioisotope Tracer Method * *Division of Nutrition, Food and Drug Administration, Washington, D. C.

“…The accuracy of the method is considered satisfactory because all final results by this method are referred back to a reference sample of cyanocobalamiu. Table 11 lists the ratios of absorbance a t 361 mp (11). In the method sent to the collaborators a range for the ratios of absorbance at 361 mp to that at 550 mp was arbitrarily selected of 3.0 to 3.5.…”

Radioisotopes in the Pharmaceutical Sciences and Industry

“…However, a few selected papers will be cited here for purposes of discussion of the methods to point up their applications. Examples, to cite a few, of medicinal analyses using radioisotopic methods include vitamins (110,111), steroids (112, 113), antibiotics (114-1 16), insecticides (117)(118)(119), barbiturates (120), the sulfa drugs (121), intrinsic factor (122,123), and salicylic acid (124,125). The most excellent example of the use and acceptance of the radioisotopic method is in the analysis of vitamin B12 (cyanocobalamin).…”

“…The most excellent example of the use and acceptance of the radioisotopic method is in the analysis of vitamin B12 (cyanocobalamin). The method described by Bacher, et al (126), involving organic solvent extraction, ion exchange, and the use of a radioactive vitamin B12-tracer has met all the tests of an excellent analytical procedure. With vitamin BIZ cobaltm available as a tracer, it is possible to assay complicated media for cyanocobalamin or total cobalamins and represents the most discriminating analysis available to date for these materials.…”

Countercurrent Analysis of Vitamin B12*

“…Chemical assays of Boxer (2), Rudkin and Taylor (ll), and Fisher (4) have been shown to be nonspecific (3) ; however, the radioactive tracer assay of Bacher (1) has been shown to be a highly specific and accurate assay for cyanocobalamin, or cobalamins easily convertible to cyanocobalamin. Of all the currently proposed assays, the radioactive tracer assay is the most accurate and specific.…”