Terahertz spectral characterization of L-carnitine derivatives: combined experimental study using microfluidic technology and density functional theory calculations

Terahertz (THz) spectroscopy is an effective method for material analysis, as molecules exhibit unique fingerprint spectra in this band. L-carnitine, a vitamin-like nutrient widely used in weight-loss health foods and nutritional additives, was investigated. Using THz time-domain spectroscopy (THz-TDS) and microfluidic chips, we measured the solid and solution absorption spectra (0.3–2.5 THz) of Acetyl-L-Carnitine Hydrochloride (ALC-HCL) and L-Carnitine L-Tartrate (LCLT). Results showed distinct spectral characteristics despite structural similarities. Density functional theory simulations identified the molecular vibrations and origins of the absorption peaks. A correlation was observed between the solid and solution states. This research provides a reference for analyzing food nutritional additives.