Rotating disk sorptive extraction of Cu-bisdiethyldithiocarbamate complex from water and its application to solid phase spectrophotometric quantification.

This study demonstrates the first use of polydimethylsiloxane (PDMS) immobilized on a rotating disk for the extraction of copper from aqueous matrices and its subsequent direct determination by solid phase UV-Visible spectrophotometry. To accomplish the solid-phase extraction and the direct solvent-free spectrophotometric measurement, sodium diethyldithiocarbamate (NaDDTC) was used as an analytical reagent to form the uncharged chromophore complex Cu(DDTC)2, which absorbs at 432 nm. Different physicochemical conditions (pH, temperature, reagent concentration, chemical modifiers) and hydrodynamic factors (rotation velocity, extraction time, sample volume) were optimized. Under the optimized conditions, extraction equilibrium times of 30, 53 and 90 min were obtained for 100, 500 and 1000 mL of sample, respectively, with preconcentration factors of 286, 712 and 1284, respectively. The methodology was precise (repeatability and reproducibility of 7.2 and 8.4%, respectively, as relative standard deviation) and accurate (recovery of 96.7%) when analyzing a multielement certified reference standard. The latter study also confirmed the high selectivity of the extraction and determination of the copper chromophore over other metal ions. The obtained limits of detection and quantification reached values lower than 12 μg L(-1), which can be reduced further by increasing the sample volume. Accuracy was also assessed using both recovery tests on drinking water matrices (95.5% recovery) and comparison with results obtained by an independent method using inductively coupled plasma-optical emission spectroscopy (ICP-OES); no significant differences were observed.