Microbiological Assay of Riboflavin

Abstract

IN his letter appearing under the above title¹, Dr. F. C. Happold criticizes the procedure used by Dr. E. C. Barton-Wright and Mr. R. G. Booth² in the determination of riboflavin, and insists on the importance of calcium in the nutrient medium and mentions the work of Chattaway, Happold and Sandford³. The evidence in the latter paper to which he evidently refers consists in an experiment in which a series of increasing doses of calcium chloride was added to the nutrient medium. The authors do not seem to have appreciated fully a limiting factor in the very low solubility of calcium in the presence of excess of phosphate at pH 6.6–6.8. The solubility product of tricalcium phosphate is about 10³², but may be perhaps 10³¹ in the presence of the other minerals contained in Chattaway, Happold and Sandford's nutrient medium^4,5.