New colorimetric method for folic acid assay in dosage forms

A new colorimetric method has been developed for estimating folic acid. The British Pharmacopoeial method has been modified to reduce folic acid to 2,4,5-triamino-6-hydroxy-pyrimidine (TAHP), which is treated with ninhydrin to yield a stable purple complex. Participation of 5-amino and 6-hydroxy groups of TAHP in the color reaction with ninhydrin is suggested on the basis of experimental evidence. The color obtained has an absorbance maximum at 555 nm and obeys Beer's law in the concentration range of 4.5 to 45 microng folic acid/ml. The method has been successfully used for assaying folic acid, its tablets, and injections.