Liquid–liquid extraction method for the gas chromatography – mass spectrometry analysis of volatile fatty acids in wastewater

This study addresses the need to transition WWTPs from energy-intensive operations to carbon-neutral and energy-efficient systems by examining VFAs' concentrations, which vary significantly with different types of wastewater. The analytical performance of the liquid–liquid extraction (LLE) method using two solvents – methyl-tert-butyl ether (MTBE) and dichloromethane (DCM) – followed by injection into a gas chromatography-mass spectrometry (GC-MS) system is evaluated. The limit of quantification (LOQ) and limit of detection (LOD) for VFAs ranged from 3 to 7.41 mg/L and 0.91 to 2.25 mg/L, respectively. Precision for lower VFAs (ethanoic (C2), propanoic (C3), 2-methyl-propanoic (iC4), butanoic (C4), methyl-butanoic (iC5), and pentanoic acids (C5)) using DCM and MTBE ranged from 1.99% to 8.64% and 1.21% to 6.68%, respectively, with accuracies of 90.35% to 107.27% and 81.55% to 105.96%, respectively. For higher VFAs (iC6, C6, and C7) using DCM, precision ranged from 18.44% to 27.06%, and accuracy ranged from 70.1% to 101.4%. In contrast, MTBE failed to detect VFAs iC6, C6, and C7. These findings underscore the importance of solvent selection in VFA analysis and its implications for optimising WWTP operations.