Development of a hollow fibre liquid phase microextraction method to monitor the sonochemical degradation of explosives in water

A novel method for the enrichment of nitroaromatic compounds present in water samples is presented here coupling hollow fibre liquid phase microextraction (LPME) with gas chromatography. A hydrophobic porous polypropylene hollow fibre was used as the interface between the donor water sample and microvolumes of the acceptor organic phase. Parameters such as extraction solvent, stirring rate, salt concentration and sampling time were studied and optimised. Overall, extraction of 11 nitroaromatics was achieved by exposing 3 μl of toluene for 20 min in a 5 ml stirred aqueous solution at room temperature. The developed protocol yielded a linear calibration graph in the concentration range 10-500 μg l-1 and the limits of detection were calculated to range between 0.29 and 0.87 μg l-1. Precision expressed in terms of relative standard deviation varied between 6.1 and 11.8%. The developed hollow fibre LPME method was subsequently used successfully to monitor the sonochemical degradation of an aqueous solution containing 100 μg l-1 of each target analyte at an ultrasonic frequency of 80 kHz. Ultrasonic treatment was found capable of efficiently removing the 2-, 3- and 4-nitrotoluene isomers as well as the 2- and 4-amino dinitrotoluene isomers within 300 min of irradiation. The rest of the analytes were more recalcitrant and significant removal was not observed even after prolonged times of ultrasonic irradiation