OPTIMIZATION AND VALIDATION OF LIQUID-LIQUID EXTRACTION (LLE) METHOD AND THE APPLICATION OF GAS CHROMATOGRAPHY WITH FID DETECTOR FOR THE DETERMINATION AND QUANTIFICATION OF VOLATILE FATTY ACIDS IN EFFLUENTS FROM ANAEROBIC REACTORS

Abstract

Controlling the chemical parameters of the anaerobic digestion (AD) process is essential for the bioconversion of organic matter to methane; among these parameters include the presence and concentration of volatile fatty acids (VFAs). It is thus necessary to use efficient analytical methods that are capable of identifying and quantifying VFAs in reactor effluents in order to obtain an immediate response to their conditions. In this study, the liquid-liquid extraction (LLE) method was optimized and validated - through an adaptation of the official method, using acetone and KHSO4, and gas chromatography with flame ionization detector (GC-FID) was used for the determination of acetic, propionic, isobutyric, butyric, isovaleric and valeric acids present in the effluents. The limit of detection (LOD) and limit of quantification (LOQ) obtained were 1.2-2.5 mg L-1 and 1.9-3.7 mg L-1, respectively, for all analytes. These low LODs and LOQs are essentially important because the presence of isobutyric and isovaleric acids above 5.0 mg can be considered indicative of imbalances in AD. The proposed method, which presented satisfactory results with good repeatability (4.2-20.7%) and recovery (90.9-104.0%) rates, was applied for the analysis of effluent samples from three continuous stirred-tank reactors (CSTR).