Determination of silver in seawater by the direct analysis of solvent bars by high resolution continuum source solid sampling graphite furnace atomic absorption spectrometry

Abstract

The direct analysis of solvent bars used for silver micro-extraction from seawater samples by high resolution continuum source solid sampling graphite furnace atomic absorption spectroscopy (HR-CS-SS-GF-AAS) has been achieved. Three successive pyrolysis steps at 290 °C, 700 °C and 1000 °C were applied to ensure the elimination of the fumes released during the calcination of the bar prior to the atomization at 1800 °C. Silver micro-extraction with solvent bars was optimised by applying a multivariate strategy. The concentrations of the extracting agent (tri-isobutylphosphine sulphide), reextracting reagent (sodium thiosulfate) and nitrate were studied by using a central composite design based on the surface response methodology. The optimum values were 0.168 mol L⁻¹, 0.033 mol L⁻¹ and 0.159 mol L⁻¹, respectively. Under these conditions, a stirring rate of 1000 rpm and an extraction time of 20 minutes were optimum. Additionally, the effect of chlorides and humic acids was also studied. The method exhibited a repeatability and reproducibility of 1.54% and 2.68%, respectively, with a limit of detection of 2.52 ng L⁻¹ and a linear range up to 334 ng L⁻¹. For the first time, an ultra-trace element (silver at the ng L⁻¹ level) was pre-concentrated and determined in seawater by using a direct solid analysis-based method, simplifying the sample preparation process and avoiding its manipulation. The method was successfully applied to dissolved silver determination in real seawater samples after the micro-extraction process and was validated by comparison with the reference method of liquid–liquid extraction with APDC/DDDC and ICP-MS determination.