In this paper, a simple and sensitive method for the determination of hydroxyl radicals generated in advanced oxidation processes is described. The proposed method employed the reaction between hydroxyl radicals and dimethyl sulfoxide (DMSO) to generate quantitatively formaldehyde, which then reacted with 2,4-dinitrophenylhydrazine (DNPH) to form the corresponding hydrazone (HCHO-DNPH) and analyzed by liquid chromatography-UV. Factors affecting the derivatization reaction of HCHO and trapping reaction of hydroxyl radicals, as well as the applicability of the method, were investigated. The detection limit for hydroxyl radicals was 0.54 mol L −1 . The method had been used to determine the yield of hydroxyl radicals in various advanced oxidation processes (AOPs) to compare their oxidation ability.

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The 1-octyl-3-methylimidazolium hexafluorophosphate ([C 8 MIM][PF 6 ]) ionic liquid was immobilized in the pores of a polypropylene hollow fiber for hollow fiber-protected liquid-phase microextraction. Analytes including 4-chlorophenol (4-CP), 3-chorophenol (3-CP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) were extracted into this ionic liquid membrane, and back extracted into 10 L sodium hydroxide acceptor solution in the lumen of the hollow fiber. Then, the acceptor solution was withdrawn into the high-performance liquid chromatography (HPLC) microsyringe connected to the hollow fiber, and directly injected into the HPLC system for analysis. Some parameters that might affect the extraction efficiency were optimized, and low detection limits (0.5 g L −1 for 4-CP, 3-CP, DCP and 1.0 g L −1 for TCP) were obtained. Good repeatability was achieved because of the stability of the hollow fiber-supported ionic liquid membrane. The proposed procedure was applied for direct determination of the four chlorophenols in some real water samples including groundwater, river water, wastewater and tap water. All of the four chlorophenols in these water samples were under the limits of determination, and the recoveries were in the range of 70.0-95.7% at 5 g L −1 spiked level.