Abstract

A procedure is described for the determination of the separate amounts of two gamma-emitting radioisotopes present simultaneously in large liquid volumes using an annular cell placed over a standard well-type crystal of sodium iodide and a reference source of ¹³⁷Cs. This sensitive technique is illustrated with particular reference to the double radioisotope urinary excretion test, using orally administered ⁵⁷CoB₁₂ bound to human gastric juice and ⁵⁸CoB₁₂ simultaneously, for the differentiation between patients with intrinsic factor deficiency and other causes of vitamin B₁₂ malabsorption.