A new contamination-free method for the determination of traces of anthropogenic silver in freshwaters

The use of different products containing silver in anthropic activities has caused the increase of silver concentrations in many water courses. To establish their toxic effects, both precise and accurate analytical methods are needed to quantify silver at very low concentrations. Although different methods may be found in the literature, in practice, most chemists or other environmentalists use solvent extraction methodology in a Clean Lab, which is tedious and with high risk of sample contamination during manipulation. In this work, the applicability of a liquid membrane-based method was studied as an alternative for the analysis of silver in freshwaters using triisobutylphosphine sulphide, TIBPS (Cyanex 471X^©), as a carrier. Transport conditions were studied and optimised; including pH and co-ion (nitrate) concentration in sample, the influence of anionic species present in freshwaters, and concentrations of carrier and stripping reagent. Under optimum conditions an extraction efficiency of 59.5% was achieved after a 4-hours operation time. Since both extraction and back-extraction processes are carried out simultaneously and without sample manipulation, this system offers a clean alternative (avoiding contamination) for determination of traces and ultra-traces of silver in freshwaters. The system was successfully applied to the preconcentration of silver, in tap and freshwater samples, before their quantification by flame atomic absorption spectroscopy (FAAS) at a ppb-level or by inductively coupled plasma-mass spectrometry (ICP-MS) at the ppt-level.