Headspace liquid-phase microextraction using ionic liquid as extractant for the preconcentration of dichlorodiphenyltrichloroethane and its metabolites at trace levels in water samples

A novel technique, high temperature headspace liquid-phase microextraction (HS-LPME) with room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]) as extractant, was developed for the analysis of dichlorodiphenyltrichloroethane (p,p′-DDT and o,p′-DDT) and its metabolites including 4,4′-dichlorodiphenyldichloroethylene (p,p′-DDE) and 4,4′-dichlorodiphenyldichloroethane (p,p′-DDD) in water samples by high performance liquid chromatography with ultraviolet detection. The parameters such as salt content, sample pH and temperature, stirring rate, extraction time, microdrop volume, and sample volume, were found to have significant influence on the HS-LPME. The conditions optimized for extraction of target compounds were as follows: 35% NaCl (w/v), neutral pH condition, 70 °C, 800 rpm, 30 min, 10 μL [C₄MIM][PF₆], and 25 mL sample solutions. Under the optimized conditions, the linear range, detection limit (S/N = 3), and precision (R.S.D., n = 6) were 0.3-30 μg L⁻¹, 0.07 μg L⁻¹, and 8.0% for p,p′-DDD, 0.3-30 μg L⁻¹, 0.08 μg L⁻¹, and 7.1% for p,p′-DDT, 0.3-30 μg L⁻¹, 0.08 μg L⁻¹, and 7.2% for o,p′-DDT, and 0.2-30 μg L⁻¹, 0.05 μg L⁻¹, and 6.8% for p,p′-DDE, respectively. Water samples including tap water, well water, snow water, reservoir water, and wastewater were analyzed by the proposed procedure and the recoveries at 5 μg L⁻¹ spiked level were in the range of 86.8-102.6%.