Determination of vitamin B12 in gruel by a radioisotope dilution assay.

The results obtained by a radioisotope dilution (RID) method for the determination of vitamin B12 in gruel were compared with those obtained by a standard microbiological assay with Lactobacillus leichmannii. A commercially available RID assay kit was used. A very high correlation between the results from the RID method and the microbiological method was found when the extraction procedure was the same. Digestion with buffer solution at pH 4.6 was shown to be the most suitable extraction method. The RID assay is an acceptable method for routine determinations of vitamin B12 in gruel.