Cloud point extraction and spectrophotometric determination of mercury species at trace levels in environmental samples

Abstract

A new micelle-mediated separation and preconcentration method was developed for ultra-trace quantities of mercury ions prior to spectrophotometric determination. The method is based on cloud point extraction (CPE) of Hg(II) ions with polyethylene glycol tert-octylphenyl ether (Triton X-114) in the presence of chelating agents such as 1-(2-pyridylazo)-2-naphthol (PAN) and 4-(2-thiazolylazo) resorcinol (TAR). Hg(II) ions react with both PAN and TAR in a surfactant solution yielding a hydrophobic complex at pH 9.0 and 8.0, respectively. The phase separation was accomplished by centrifugation for 5min at 3500rpm.The calibration graphs obtained from Hg(II)–PAN and Hg(II)–TAR complexes were linear in the concentration ranges of 10–1000μgL−1 and 50–2500μgL−1 with detection limits of 1.65 and 14.5μgL−1, respectively. The relative standard deviations (RSDs) were 1.85% and 2.35% in determinations of 25 and 250μgL−1 Hg(II), respectively. The interference effect of several ions were studied and seen commonly present ions in water samples had no significantly effect on determination of Hg(II). The developed methods were successfully applied to determine mercury concentrations in environmental water samples. The accuracy and validity of the proposed methods were tested by means of five replicate analyses of the certified standard materials such as QC Metal LL3 (VWR, drinking water) and IAEA W-4 (NIST, simulated fresh water).