Sensitive determination of mercury in tap water by cloud point extraction preconcentration and flow injection-cold vapor-inductively coupled plasma optical emission spectrometry

ALTAMIRANO, JORGELINA C.; WUILLOUD, RODOLFO G.; SILVA, MARIA F.; OLSINA, ROBERTO A.; MARTINEZ, LUIS D.

Florianópolis

Simposio; SEVENTH RIO SYMPOSIUM ON ATOMIC SPECTROMETRY; 2002

Universidade Federal de Santa Catarina

The determination of mercury is very important in environmental and toxicological studies. One of the routes of incorporation of mercury into the human body is drinking water. Hence, its determination in this type of samples becomes very important. Since mercury concentrations in nonpolluted waters are very low, powerful techniques are required and only few of them show enough sensitivity. Different analytical methods have been developed for the determination of mercury at low concentrations, but the most commonly used ones are cold vapor atomic absorption spectrometry (CV-AAS), cold vapor atomic fluorescence spectrometry (CV-AFS), flow injection-inductively coupled plasma optical emission spectrometry (FI-ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS).Although CV-AAS and ICP-OES are the most used techniques in the determination of traces of mercury, the low concentration level of mercury in water is not compatible with the detection limit of these techniques. In order to achieve accurate, reliable and sensitive results, preconcentrations and separations are needed when the concentrations of analytes in the sample are too low to be determined directly by ICP-OES even with mercury vapor generation. A scheme of preconcentration can thus be proposed, mediated by surfactants (CPE, cloud point extraction) instead of organic solvents. Above the cloud point (temperature at which this phase behavior occurs), the solution is separated into two phases; one, the aqueous phase that contains the surfactant at a concentration close to the critical micellar concentration (cmc), and the other, the surfactant-rich phase, which volume is very small. Any species initially present in the solution that interact with the micellar aggregates are thus extracted and may be preconcentrated in the small volume of the surfactant-rich phase.In the present work, a preconcentration and determination methodology for mercury at trace levels in water samples was developed. Cloud point extraction was successfully employed for the preconcentration of mercury prior to inductively coupled plasma atomic optical emission spectrometry (ICP-OES) coupled to a flow injection (FI) with cold vapor (CV) generation system. The mercury was extracted as mercury-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol [Hg(II)-(5-Br-PADAP)] complex, at pH 9.2 mediated by micelles of the non-ionic surfactant polyethyleneglycolmono-p-nonyphenylether (PONPE-5). Cold vapor generation was developed from 100 uL of the extracted surfactant-rich phase by means of a stannous chloride (SnCl2) solution as reductant. The 50 mL sample solution preconcentration allowed to raise and enrichment factor of 200-fold. The lower limit of detection (LOD) obtained under the optimal conditions was 4 ng/L. The method was successfully applied to the determination of mercury in tap water samples.