Competitive protein-binding radioassay of thiamine in simple solutions and in multivitamin pharmaceuticals

A competitive inhibition radioassay of thiamine is described using a gel obtained by coupling a buckwheat-seed thiamine-binding protein to CNBr-activated Sepharose. The sample to be analysed is incubated with gel suspension and [14C]thiamine and after centrifugation the radioactivity of the supernatant is measured. The method is simple and specific, and applicable over a thiamine concentration range 0.5-5 microM with a coefficient of variation typically below 5%. The gel is reusable and stable for several months. Applicability of the method for direct determination of thiamine in multivitamin pharmaceuticals is demonstrated.