Orthogonal array optimization of ultrasound-assisted emulsification-microextraction for the determination of chlorinated phenoxyacetic acids in river water.

Orthogonal array design (OAD) was utilized for the first time to optimize the experimental conditions of ultrasound-assisted emulsification-microextraction (USAEME) for determining chlorinated phenoxyacetic acids (CPAs) in river water samples. The use of ultrasound facilitates the mass transfer of CPAs from an aqueous phase into a water-immiscible organic extraction solvent (dichloromethane, DCM) without adding dispersive solvent to form numerous microdroplets. The water-immiscible extractant was collected by centrifugation, dried under low pressure, reconstituted in methanol-water mixture (1:1), and injected into a HPLC system for the determination of CPAs. The linear range was 2-1000 ng mL(-1) (2, 5, 10, 50, 200, 500 and 1000 ng mL(-1)) for each analyte and the relative standard deviations of CPAs among the seven different concentrations were in the range of 1.5-17.0% (n=3). The detection limits (signal-to-noise ratio of 3) of CPAs ranged from 0.67 to 1.50 ng mL(-1). The ranges of intra-day precision (n=3) for CPAs at the levels of 5 and 200 ng mL(-1) were 3.6-11.9% and 5.3-9.5%, respectively. The range of inter-day precision (n=3) at 5 and 200 ng mL(-1) were 1.4-7.7% and 8.5-12.2%, respectively. The applicability of USAEME for environmental analysis was demonstrated by determining CPAs in river water. The recoveries of CPAs from five-spiked river water samples at 10 and 200 ng mL(-1) were 96.3-112.5% and 94.8-109.4%, respectively. The maximum contaminant level (MCL) of 2,4-D in drinking water and the tolerance of residues in food for p-CPA are 70 and 200 microg L(-1), respectively, according to the US EPA regulations. These contaminant levels fall in the linear range investigated in this study. In addition, this USAEME method provided detection limits lower than their contaminant levels, which made USAEME an effective sample preparation method for determining organic environmental contaminants, such as CPAs, in river water samples with little consumption of organic solvent.