Determination of aqueous chlorothalonil with solid-phase microextraction and gas chromatography

Solid-phase microextraction coupled with GC-electron-capture detection was examined to analyze aqueous chlorothalonil residuals. The optimal conditions for chlorothalonil pre-concentration such as fiber polarity, temperature, salt addition, absorption time, as well as the interference were investigated in detail. In addition, the thermal desorption conditions in the injector were also systematically optimized. Experimental results indicated that an extraction with a 100-microm polydimethylsiloxane fiber for 40 min under conditions of 1250 rpm stirring rate, room temperature, and adding high concentration salt offered an optimal result. The thermal desorption of chlorothalonil at 240 degrees C for 3 min (including fiber regeneration) offered the best sensitive detection. A standard addition method for calibration was recommended to reduce the deviation from matrix interference. The proposed method provided a simple and rapid analytical procedure for chlorothalonil in water bodies with detection limits of 2.86 microg/l for distilled water, 3.06 microg/l for ground water, 4.77 microg/l for tap water, and 9.23 microg/l for farm water. The relative standard deviations were all below 3.0% (n=6) besides the farm water being below 9.2%. The calibration graph in the range of 5 to 200 microg/l is linear with very good correlation coefficient (r=0.999), and r=0.983 for farm water. Application was illustrated by the analysis of water samples collected from tap water, ground water and farm water in the southern Taichung area.