Controlled Silica Hydration Enables Mechanism-guided Green Solid-Phase Extraction for Steryl Glucoside Determination in Biodiesel.

Steryl glucosides are minor lipid contaminants in biodiesel that can cause fuel filter plugging and adversely affect fuel quality, even at trace concentrations. Reliable determination of steryl glucoside is therefore essential for biodiesel quality control. Solid-phase extraction (SPE) is widely used for sample pretreatment prior to chromatographic analysis; however, conventional silica-based SPE protocols typically require hazardous organic solvents for cartridge preconditioning. In this study, a controlled silica hydration-based SPE method was developed for the pretreatment of steryl glucoside in crude biodiesel prior to high-performance size-exclusion chromatography coupled with evaporative light-scattering detection using a 100-Å Phenogel column. The effect of water volume (0.05-0.50 mL) used for silica preconditioning was systematically investigated. Following SPE, retained steryl glucoside was recovered by heptane washing and elution with acetone/methanol (9:1, v/v). Preconditioning with 0.075 mL of water provided the highest steryl glucoside concentration (106.29 µg/mL), approximately four times the concentration obtained with non-preconditioned silica (27.06 µg/mL) and substantially higher than those obtained with conventional heptane- (53.70 µg/mL) and acetone/methanol-preconditioned (76.73 µg/mL) cartridges. The method exhibited limits of detection and quantification of 8.07 and 24.47 µg/mL, respectively. The enhanced extraction efficiency is attributed to controlled hydration of surface silanol groups, which establishes a balanced physicochemical environment favorable for steryl glucoside adsorption while substantially reducing the consumption of hazardous organic solvents. The proposed controlled silica hydration-based SPE method provides a simple, environmentally friendly, and mechanistically guided pretreatment strategy for the determination of steryl glucoside in biodiesel and may also be applicable to the extraction of other polar lipid analytes.