Matrix Solid-Phase Dispersion Based on Carbon Nanotube Coupled with Dispersive Liquid–Liquid Microextraction for Determination of Organochlorine Pesticides in Soil

The presented article describes the methodology and results of investigating the capability of multi-walled carbon nanotube as sorbent in an efficient extraction method for determination of organochlorine pesticides, α-BHC, β-BHC, γ-BHC, heptachlor, endrin, aldrin, 4,4'-DDD, 4,4'-DDE and 4,4'-DDT, in soil media. Matrix solid-phase dispersion was optimized for extraction from small amounts of soil samples and the resulting extracts were pre-concentrated using dispersive liquid-liquid microextraction. The most important experimental parameters of both extraction procedures were studied and the optimum conditions for simultaneous analysis of the target analytes were determined. In the final analysis procedure, a 0.20 g portion of dried soil sample was extracted by dichloromethane after being mixed with 0.020 g of carbon nanotube and 0.400 g of silica gel. Then, dispersive liquid-liquid extraction was used to pre-concentrate the extract before injecting the sample into the gas chromatographic system. The pre-concentration step showed to have up to 32 times of enrichment capability and the total procedure had reasonable sensitivity and reproducibility, with limit of detections <1.6 ng g-1 and relative standard deviation values below 8.1%, respectively. It was also demonstrated that the organic content of the soil can alter the extraction efficiency (70-105%), depending on both the amount of the organic matter and the individual analyte. Therefore, the importance of matrix spike samples, throughout the method validation procedure, was confirmed.