A new approach to the determination of folic acid at trace levels: using a Fe(iii)-folic acid complex to amplify analytical signal

Abstract

A fast, efficient, cost-effective, and environmental-friendly analytical methodology was developed for preconcentration and determination of trace folic acid in food samples prior to high performance liquid chromatography with diode array detection (HPLC-DAD). The method is based on formation of stable complexes between folic acid and Fe(III) ions at pH 8.0. The formed complexes were extracted to a nonionic surfactant phase containing PONPE 7.5. The surfactant rich phase (SRP) was separated by decantation and diluted with 300 μL of a mixture of 1 M HCl and methanol at a 1 : 1 ratio. The parameters and variables that affected the method were also investigated and optimized in detail. The limit of detection (LOD) of folic acid was 6.06 ng mL⁻¹, the linear range of quantitation for folic acid was 20–1200 ng mL⁻¹ and the correlation coefficients of the calibration curves were 0.9976. The average recoveries and relative standard deviations in the analysis of real samples were in the range of 95.1–105.1% and 1.73–5.25%, respectively. After validation of the method was carried out, the method was applied to the determination of folic acid in real samples, including baby foods, vegetables, cereals, and pharmaceutical samples.