Solid-phase microextraction in combination with GC-FID for quantification of the volatile free fatty acids in wastewater from constructed wetlands

A headspace solid-phase microextraction (HS-SPME) followed by gas chromatography coupled to flame ionization detector (GC-FID) is developed for the direct determination of volatile fatty acids (VFAs) in wastewater from constructed wetlands. Through the investigation on extraction behavior of different coatings for VFAs and the chromatographic behavior of VFAs in a Stabilwax-DA capillary column (30 m x 0.32 mm i.d., 0.25 μm film thickness) using nitrogen as carrier gas, the polyacrylate fiber is selected as the satisfactory coating for VFAs analysis, and optimum chromatographic conditions are obtained. The oven temperature is programmed at 70°C for 2 min, then a 4°C/min rate until 180°C, holding 2 min, and then a 20°C/min rate until 200°C, holding the final temperature for 3 min. The various parameters including extraction time, extraction temperature, pH value, ion strength, sample volume, and desorption conditions are investigated for the optimization of HS-SPME performance for VFAs in the wastewater. The experimental results show that the linear dynamic ranges are 10-45000 μg/L, and over two to four orders of magnitude depending on different acids. The detection limit (3σ) for VFAs are low to μg/L levels and the relative standard deviations are less than 10%, and the recoveries are between 85% and 117%. By using 2-ethylbutyric acid as internal standard, the proposed method is successfully applied to the determination of VFAs in wastewater from the constructed wetlands.