Formation, occurrence and determination of volatile fatty acids in environmental and related samples

Volatile fatty acids (VFA) are short chain aliphatic monocarboxylic acids containing from 2 to 8 carbon atoms in a molecule. They are formed in the process of anaerobic biodegradation of larger organic molecules and therefore are commonly present in municipal wastewater, effluents of food industry, livestock farm wastewater, sewage sludge, landfill leachate, feces, urine, etc. and are emitted by some animals and higher plants. VFAs play an important role in biological wastewater treatment and are important intermediates in conversion of organic waste into methane. When discharged into the environment, VFAs can have some harmful effects. Different separation techniques have been used to determine individual VFAs, most often gas chromatography (GC), which can separate VFAs either as free acids or as their derivatives, but also liquid chromatography and electrophoresis. Relatively clean aqueous samples can be directly injected into GC for analysis. In the case of solid samples, “dirty” aqueous samples and trace analytes concentrations in the air VFAs must be first isolated and possibly enriched before the analysis proper. Solvent extraction (SE), headspace (HS), solid phase microextraction (SPME) and HS-SPME for condensed phases and sorbent trapping and SPME for gaseous samples have been generally used to prepare the sample for the analysis.