Eliminating the matrix effects of dissolved carbon dioxide and carbonate in extraction of triclosan and chlorophenols in environmental waters by hollow fiber supported liquid membrane

Abstract

Hollow fiber supported liquid membrane (HFSLM) extraction often suffers from matrix effects in extracting weak organic acids in environmental waters, but the reasons for which are unclear. This work systematically studied the influence of dissolved carbon dioxide and carbonate on the HFSLM extraction of analytes in environmental waters, by using triclosan and its two typical degradation products, 2,4-dichlorophenol and 2,4,6-trichlorophenol, as model compounds. HFSLM was conducted by immersing a HFSLM extraction device into a 200 mL water sample modified with 0.01 M HCl and 10% (m/v) NaCl, and shaking at 250 rpm for 90 min. The extraction device was prepared by immobilizing dihexyl ether on the polypropylene hollow fiber membrane wall (60 cm length, 50 μm wall thickness, 280 μm inner diameter), filling the fiber lumen with 0.4 M NaOH as acceptor, and closing the two ends of the fiber with aluminum foil. It was demonstrated that the dissolved carbon dioxide and carbonate present in environmental samples reduces the acceptor pH and thus the recovery of target analytes, and purging the acidified sample with ∼50 mL min⁻¹ N₂ for 15 min is a very efficient approach to eliminate this matrix effect. With this purging pretreatment, the recoveries of the analytes in environmental samples increased substantially from below 40% to between 63% and 121%. For the three analytes, the proposed HFSLM method provided enrichment factors in the range of 1090–1322, and detection limits in the range of 0.1–0.2 μg L⁻¹ by coupling with an ultra-performance liquid chromatography-mass spectrometry system.