A handling-free methodology for rapid determination of Cu species in seawater based on direct solid micro-samplers analysis by high-resolution continuum source graphite furnace atomic absorption spectrometry

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.