HPTLC Screening of Folic Acid in Food: In Situ Derivatization with Ozone-Induced Fluorescence

Abstract

This paper proposes a facile and specific method tailored for quantifying and confirming folic acid in food, based on the combination of high-performance thin layer chromatography with fluorescence densitometry and surface-enhanced Raman spectroscopy. Chromatography was carried out on silica gel plates, using methanol/ethyl acetate/ammonia (6:4:1, v/v/v) as the mobile phase. For the first time, ozone gas was utilized as the derivative agent, which efficiently induced the appearance of strong fluorescence of the analyte. Thereafter, fluorescent densitometry measurements were carried out for quantitative purpose, offering good linearity (R2 > 0.999) and sensitivity (0.7–1.4 mg/kg). In addition, the applicability and reliability of the established method was validated with food and food supplement samples, showing good agreement with the data obtained by conventional HPLC-UV as the benchmark, but with remarkably higher efficiency. Apart from that, the in situ-obtained surface-enhanced Raman spectroscopic fingerprint of bands under optimized conditions (532-nm incident laser and tenfold concentrated silver nanoparticles) enabled unambiguous identification of the targeted compound, serving as a convenient and affordable tool to prevent potential mistake from false-positive results.