Dispersive liquid–liquid microextraction of trace Hg2+ for visual and fluorescence test

In this work, trace Hg2+ in environmental water samples was first preconcentrated by dispersive liquid–liquid microextraction (DLLME), and then was colorated by one common rhodamine B thiolactone (RBT) probe for visual and fluorescence detection. In this way, a highly sensitive and selective method was developed for field monitoring of Hg2+ in environmental waters. The color of RBT test solution could change clearly from colorless to pink around the level of 2 μg L−1 Hg2+, which just meets with the maximum residue level of Hg2+ in drinking water recommended by U.S. EPA, so the water samples with Hg2+ concentration over 2 μg L−1 could be selected rapidly by naked eye. Moreover, the quantification of Hg2+ could be obtained by fluorescence detection of test solution. The best extraction efficiency of Hg2+ by DLLLME could be obtained by using 200 mL water sample (pH 5.0, 50 °C), 150 μL extraction solvent (lauric acid, LA) and 3 mL dispersive solvent (methanol). Thus an enrichment factor of ∼407 and the limit of fluorescence detection of 0.03 μg L−1 could be achieved. The method was also highly selective for Hg2+ with tolerance to at least 1000-fold of the foreign metal ions. This method was successfully applied to detect Hg2+ in deionized water, tap water and sea water.