Determination of trihalomethanes in drinking water by dispersive liquid-liquid microextraction then gas chromatography with electron-capture detection

Dispersive liquid-liquid microextraction (DLLME) has been used for preconcentration of trihalometkanes (THMs) in drinking water. In DLLME an appropriate mixture of an extraction solvent (20.0 mu L carbon disulfide) and a disperser solvent (0.50 mL acetone) was used to form a cloudy solution from a 5.00-mL aqueous sample containing the analytes. After phase separation by centrifugation the enriched analytes in the settled phase (6.5 +/- 0.3 mu L) were determined by gas chromatography with electron-capture detection (GC-ECD). Different experimental conditions, for example type and volume of extraction solvent, type and volume of disperser solvent, extraction time, and use of salt, were investigated. After optimization of the conditions the enrichment factor ranged from 116 to 355 and the limit of detection from 0.005 to 0.040 mu g L-1. The linear range was 0.01-50 mu g L-1 (more than three orders of magnitude). Relative standard deviations (RSDs) for 2.00 mu g L-1 THMs in water, with internal standard, were in the range 1.3-5.9% (n = 5); without internal standard they were in the range 3.7-8.6% (n = 5). The method was successfully used for extraction and determination of THMs in drinking water. The results skowed that total concentrations of THMs in drinking water from two areas of Tehran, Iran, were approximately 10.9 and 14.1 mu g L-1. Relative recoveries from samples of drinking water spiked at levels of 2.00 and 5.00 mu g L-1 were 95.0-107.8 and 92.2-100.9%, respectively. Comparison of this method with other methods indicates DLLME is a very simple and rapid (less than 2 min) method which requires a small volume of sample (5 mL).