Emulsification-based dispersive liquid microextraction and HPLC determination of carbazole-based explosives

We have developed a method for liquid-liquid microextraction of the explosives trinitrocarbazole (TrNC), tetranitrocarbazole (TNC) and carbazole from water samples. It is based on the use of a solvent mixture that contains appropriate amounts of the extraction solvent (chloroform) and an aqueous solution of didecyl dimethyl ammonium bromide as disperser. This mixture is rapidly injected into the water sample upon which a cloudy microemulsion is formed which extracts the analytes. After centrifugation and phase separation, the sedimented phase is used for the determination of the analytes by HPLC with UV detection. Under the optimized conditions, the calibration plot is linear in the range from 0.35 to 351 ng mL(-1) for TNC, 0.30 to 305 ng mL(-1) for TrNC, and 2.1-421 ng mL(-1) for carbazole. The limits of detection, at a signal-to-noise ratio of 3, range from 0.08 to 0.10 ng mL(-1), the relative standard deviations (at n = 6) for the extraction of TNC (3.5 ng mL(-1)), TrNC (3.0 ng center dot mL(-1)) and carbazole (3.2 ng mL(-1)) vary between 5.3 and 6.1 %, and the enrichment factors range from 264 to 295.