Validated Spectrofluorometric Assay for Folic Acid Determination in Pure and Pharmaceutical Forms via Basic Fuchsin Fluorescence Quenching

A simple, specific, sensitive, rapid, and cost-effective spectrofluorometric method for quantifying folic acid has been developed using basic fuchsin as a fluorescence quenching agent. This method relies on the quenching effect of folic acid on the inherent fluorescence of basic fuchsin, facilitated by their interaction in Britton–Robinson buffer solution at pH 9, leading to the formation of an ion-associated complex. The decrease in fluorescence intensity of basic fuchsin was measured at 730 nm, with excitation at 365 nm. The method demonstrated a linear relationship (R² = 0.9977) between the quenching fluorescence intensity (ΔF) and folic acid concentration over the range of 4–20 μg/mL, with a detection limit of 0.17 μg/mL. The method showed no significant interference from common excipients found in pharmaceutical tablets. The results obtained were in good agreement with those from high-performance liquid chromatography, with no significant differences in precision or accuracy. This spectrofluorimetric method was successfully applied to determine the folic acid content in various commercial pharmaceutical tablets.