Freestanding Fully Porous Polyimide Membrane for Thin Film Microextraction

In this study, freestanding fully porous polyimide (FFPP) membranes were prepared in batches by the scraping technique and vapor-induced phase separation (VIPS) and used for thin film microextraction (FFPP-TFME). When water vapor was applied simultaneously during scraping, the resulting membrane surface was highly porous, in contrast to the dense and smooth surface obtained without vapor. The micro/nanocomposite pore structure was revealed by scanning electron microscopy and nitrogen adsorption-desorption. The diameters of the micropores, nanopores and fibrous polyimide (PI) nanofibers were 0.5-1.5 mu m, ca. 30 nm and ca. 250 nm, respectively. The extraction performance of the FFPP-TFME method was evaluated with organochlorine pesticides (OCPs) as model analytes in water. The extracted OCPs were desorbed in acetone and then quantified by gas chromatography-mass spectrometry. The effects of extraction time, ionic strength, desorption solvent, desorption volume and desorption time were investigated. Under the optimized conditions, the limits of detection (LODs) for eight OCPs (4.4-83 ng L-1), linear ranges (0.05-50 mu g L-1), correlation coefficients (0.997-0.999), intrabatch relative standard derivations (RSDs, 0.88-9.20%) and interbatch RSDs (6.35-13.5%) were obtained. The method was also successfully applied to the analysis of environmental water samples, and the relative recoveries of all real water samples were 73.6-116.4%. These results show that the FFPP-TFME method is a simple, efficient and environmentally friendly method for the pretreatment of trace organic pollutants in water samples.