Folate assay: a comparison of radioassay and microbiological methods.

Folate mono- and polyglutamate standards were assayed by a microbiological method and by four commercially available radioassay methods to evaluate the usefulness of radioassay techniques for the quantitation of naturally occurring folates. Folate monoglutamates exhibited different responses in the radioassay procedures, depending on the one-carbon constituent and oxidation state. Folate polyglutamates exhibited an increased response that varied depending on the folate concentration. The varied responses of folate mono- and polyglutamates in the radioassay procedures make this technique unsuitable for the determination of the mixture of folate derivatives that are normally encountered in biological extracts.