Search

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. [ABSTRACT FROM AUTHOR]

A very simple, sensible and advanced new methodology for the determination of copper species in seawater has been developed. The method consisted of two steps: first a separation/preconcentration of copper species by using liquid phase microextraction-based solvent bars followed by the direct analysis of these solid polymeric micro-samplers in an atomic absorption spectrometer provided with a device for direct analysis. For liquid microextraction, di-2-pyridylketone benzoylhydrazone (dPKBH) dissolved in octan-1-ol was selected as the extracting agent due to its ability to transport inorganic Cu species from seawater samples. The optimum chemical and physical conditions for copper micro-extraction were sample pH 8, a dPKBH concentration of 0.010 mol L−1, a stirring speed of 800 rpm and an extraction time of 10 min. A graphite furnace temperature program was optimised to assure the complete elimination of the solvent bar matrix, and the atomisation step took place at 2200 °C. The method exhibited a limit of detection of 0.026 μg L−1 of copper and a linear range up to 1.50 μg L−1, showing great repeatability and reproducibility (4.07% and 4.43%, respectively). Suitability of the method was confirmed by analysing a certified reference material (CASS-4) under optimum conditions, being the first time ever that a direct solid analysis-based method has been used for the determination of total dissolved copper concentration in seawater. Furthermore, the method was applied to the determination of the operationally defined transportable Cu fraction in seawater samples at natural conditions and the results were compared with theoretical data provided by Visual MINTEQ® 3.1 software. A mathematical model that permits to estimate total dissolved copper concentration was obtained, and the non-transportable copper fraction was calculated by difference. Image 1 • Direct analysis of 2SBME by SS HR-CS GF-AAS allow ultra-trace determination of copper fractions in seawater • Sample preparation process is simplified and its manipulation notably reduced. • Calibration is carried out with standards with the same sample matrix composition. • The sample and reagents consumption is reduced and waste minimized. [ABSTRACT FROM AUTHOR]