Brewing biofuel from coffee waste: Production and GC-MS/MS characterization

The growing production of spent coffee grounds (SCG) presents a valuable opportunity for sustainable biodiesel generation due to their high lipid content. This study investigates the extraction, transesterification, and analytical characterization of biodiesel derived from SCG. Lipid extraction was performed using Soxhlet and ultrasound-assisted methods with hexane, yielding 14.4% and 11.3% oil, respectively. Biodiesel was produced via conventional and ultrasound-assisted transesterification, achieving FAME yields of 70.2% and 68.9%, respectively. The resulting biodiesel met the key EN 14214 standards for density, viscosity, water content, and cold flow performance; however, the acid value and oxidative stability require further optimization. FAME composition, dominated by methyl linoleate, palmitate, and oleate, was initially assessed using GC-MS. However, co-elution among C18:1, C18:2, and C18:3 limited resolution. To address this, GC-MS/MS with Multiple Reaction Monitoring (MRM) was employed, enabling accurate identification based on distinct ion transitions. MRM mode improved sensitivity and specificity, allowing clear quantification of unsaturated FAMEs despite overlapping retention times. This work highlights SCG as a promising waste-to-biofuel feedstock and emphasizes the role of MRM-based GC- MS/MS in enhancing analytical precision for biodiesel characterization.