Liquid-phase microextraction with solidification of the organic floating drop for the preconcentration and determination of mercury traces by electrothermal atomic absorption spectrometry

A procedure for the determination of traces of mercury by liquid-phase microextraction based on solidification of a floating organic droplet for separation and electrothermal atomic absorption spectrometry for final measurement has been developed. For this purpose, 50 μL of pre-heated (50 °C) undecanoic acid (UA), are added to 25 mL of aqueous sample solution at pH 5. The mixture, maintained at 50 °C, is stirred for 10 min using a high stirring rate in order to fragment the UA drop into droplets, thus favoring the extraction process. Next, the vial is immersed in an ice bath, which results in the solidification of the UA drop that is easily separated. Injection into the atomizer is carried out after gentle heating. The pyrolytic atomizers are coated with electrolytically reduced palladium that acts as an effective chemical modifier for more than 500 firings. Under the optimized conditions, the detection limit was 70 ng L⁻¹ mercury with an enrichment factor of 430. The relative standard deviation of the measurements was in the 2.1–3.5% range. Recovery studies applied to the determination of mercuric ions in bottled and tap water samples were in the 92–104% range.