Optimization of nonequilibrium liquid-phase microextraction for the determination of nitrobenzenes in aqueous samples by gas chromatography-electron capture detection

In the present work, a novel method for the determination of nitrobenzenes in water has been described. It is based on nonequilibrium liquid-phase microextraction and gas chromatography-electron capture detection (GC-ECD). Extraction conditions such as solvent selection, organic solvent dropsize, stirring rate, content of NaCl and extraction time were found to have significant influence on extraction efficiency. The optimized conditions were 1.5 mul toluene and 20 min extraction time at 400 rpm stirring rate without NaCl addition. The linear range was 0.1 - 50 mug l(-1) for most nitrobenzenes. The limits of detection (LODs) ranged from 0.02 mug l(-1) (for 2.6-DNT) to 0.4 mug l(-1) (for NB); and relative standard deviations (RSD) for most of the nitrobenzenes at the 10 mug l(-1) level, except for 2,6-DNT in 3 mug l(-1), were below 10%. Natural samples collected from Miyun Reservoir and tap water samples from a laboratory were successfully analyzed using the proposed method, but none of the analytes were detected. The relative recoveries of spiked water samples (at the 10 mug l(-1) level except for 2,6-DNT in 3 mug l(-1)) were from 82.6 to 118.7%.