Vortex-assisted emulsification microextraction followed by in-syringe ultrasound-assisted back-microextraction to determine haloacetic acids in waters

Abstract

We have evaluated a vortex-assisted emulsification microextraction (VAEME) procedure followed by in-syringe ultrasound-assisted back-microextraction for the determination of nine haloacetic acids in waters of different nature, using high-performance liquid chromatography with diode array detection. The optimized method requires 600 μL of isopropyl ether as an extractant solvent and 5 mL of the water sample containing: Na₂SO₄ (45%, w/v) and a low pH value (<0.5). After emulsification assisted by vortex for 5 min, the droplet is separated from the water sample after centrifugation (5 min, 3500 rpm) using a syringe. This droplet is then back-microextracted in the syringe by mixing it with a low volume (50 μL) of an aqueous solution of (NH₄)₂SO₄ (0.2 M), to ensure compatibility with the HPLC mobile phase. After 5 min of sonication, the aqueous solution containing HAAs is directly injected into the chromatograph. The method is characterized by (a) average relative recoveries of 77.7–89.0%, depending on the spiked level, (b) average enrichment factors of ∼10 for the VAEME and of ∼21 for the overall method, (c) precisions of the overall method (expressed as relative standard deviations) between 5 and 23%, and (d) average extraction efficiencies of ∼88% for the VAEME method.