Ultrasound-assisted Emulsification Microextraction for Fetermination of Volatile Fatty Acids in Agricultural Wastewater Samples by Gas Chromatography Flame Ionization Detector

Abstract

Ultrasound-assisted emulsification microextraction (USAE-ME) procedure coupled with gas chromatography–flame ionization detection (GC-FID) was applied for the determination of four volatile fatty acids (VFAs), including Propionic acid, butyric acid, valeric acid, and iso-valeric acid, in water and agricultural wastewater samples. The method is based on the dispersion of microvolumes of an organic solvent in the aqueous phase and subsequent extraction of target analytes into the fine droplets of the organic phase. After centrifugation, the sedimented phase is separated and directly injected to the GC system. The effect of experimental parameters, such as type and volume of extraction solvent, equilibrium time, pH and ionic strength of the aqueous solution were investigated and optimized. Under the optimum conditions a relatively broad dynamic linear range with a good linearity (R2) ranging from 0.9960 to 0.9982 were obtained for all target analytes. The limit of detection (S/N=3) and the enrichment factors were in the range of 0.01-0.05 μg mL−1 and 410-705, respectively. The relative standard deviations (RSD %) for 2 μg mL−1 of VFAs were in the range of 5.4–6.4% (n=5).  Finally, the purposed method has been successfully applied to the determination of target VFAs in different water samples and good spiked recoveries over the range of 91–108% were obtained.