Comparison of subcritical water extraction and microwave-assisted water extraction for the determination of chlorophenols in polluted lake sediments

Abstract

Two environmentally friendly sample preparation methods, subcritical water extraction (SWE) and microwave-assisted water extraction (MAWE) coupled to the gas chromatography with electron capture detector (GC-ECD), were evaluated and optimized for the sensitive, selective and solvent-free determination of four chlorophenols (2-chlorophenol, 2,4-dichlorophenol, 4-chlorophenol and pentachlorophenol) in polluted Ya-Er Lake sediments. An orthogonal array design L₉ (3³) was applied to select the optimum conditions for SWE. The best results as regards sensitivity, repeatability and analyte recovery were obtained using SWE with 9 mL of sodium hydroxide solution (pH 9), at 150 °C for 80 min. The best extraction conditions for MAWE were obtained by using the same extractant as SWE at 900 W and 0.2 MPa for 6 min. Under final working conditions, satisfactory recoveries of individual chlorophenols (CPs) were obtained in the range of 77.7–113.0% and 83.5–104.7% for SWE and MAWE respectively. The effectiveness of the extraction conditions proposed in both methods was evaluated for the extraction of 2,4-DCP in lake sediments with different sample characteristics such as organic carbon and water content. The results indicated that sediments containing relatively low amounts of organic carbon can be quantitatively extracted by both extraction methods. For sediments with larger amounts of organic carbon, the MAWE-based method showed a little better result for analyte recovery than SWE.