Development of a Liquid–Liquid Extraction Based on Deep Eutectic Solvent for the Analysis of Steryl Glucoside in Biodiesel

The quantification of trace amounts of steryl glucoside (SG) in biodiesel presents a significant analytical challenge due to its low solubility and tendency to crystallize. This study introduces a dispersive liquid-liquid extraction method utilizing a deep eutectic solvent (DES) for the efficient pretreatment and extraction of SG from a palm oil (PO) biodiesel model. The optimized extraction conditions employed a DES composed of choline chloride and ethylene glycol (1:2 molar ratio), combined with isopropanol as a disperser solvent in a 1:1 weight ratio, and vortex-assisted mixing. High-performance size exclusion chromatography coupled with an evaporative light scattering detector was employed for the analysis of SG, using a mobile phase consisting of toluene, tetrahydrofuran, and acetic acid (100:6:0.25, v/v/v). The method demonstrated a limit of detection of 1.92 µg/mL, a limit of quantification of 5.82 µg/mL, and excellent linearity (R² = 0.9928). When applied to commercial PO biodiesel (both crude and refined), the method yielded recovery rates ranging from 86.99% to 96.97%. These results demonstrate that dispersive liquid-liquid extraction with DES is an effective and environmentally friendly approach for SG extraction and analysis in biodiesel.