Colorimetric determination of folic acid in pharmaceutical preparations

Abstract

A colorimetric method, based on colour development with 1,2-naphtho-quinone-4-sulphonic acid, sodium salt, has been developed for the determination of folic acid. The method depends on the availability of the primary amino group that is liberated on reduction of folic acid. The colour produced has an absorbance maximum at 485 nm and obeys Beer's law in the concentration range 11·7 to 58·7 µg ml^–1. The method has been used successfully for assaying folic acid, tablets containing folic acid alone or in combination with iron and vitamin B₁₂, and injections of folic acid.