HPLC–DAD analysis of functional dietary supplements followed by liquid–liquid microextraction-assisted FTIR identification of IR-active ingredients

Accurate identification of active ingredients in dietary supplements and functional beverages is essential for ensuring product quality and consumer safety. Fourier transform infrared (FTIR) spectrometry, when coupled with high performance liquid chromatography (HPLC), provides molecular information for compound characterization but is limited by solvent interference. This study presents a liquid-liquid microextraction (LLME)-assisted HPLC-FTIR method for isolating and identifying bioactive compounds in complex supplement matrices. HPLC fractions of a branched-chain amino acid beverage were subjected to LLME using infrared-transparent, non-polar solvents to remove mobile phase residues and buffer salts prior to FTIR analysis. Extraction parameters, solvent composition, and buffer effects were optimized and compared with conventional solvent evaporation. The LLME approach effectively eliminated solvent and salt interference, yielding clear spectra that enabled identification of citric acid, L-ascorbic acid, valine, leucine, isoleucine, and caffeine. The method uses standard laboratory equipment and is compatible with common chromatographic systems, offering a practical solution for routine supplement quality control and regulatory testing. This LLME-assisted HPLC-FTIR strategy provides a reliable pathway for infrared-based identification of active ingredients in complex food and pharmaceutical products.