AISIT — a new device for remote-controlled sampling of dissolved and particle-bound trace elements in surface waters

An automatic sampling device for water samples (AISIT = a utomatic i ntelligent water s ampler for i norganic t race constituents) was developed by the Becfield Company (Isernhagen, Germany) and the GKSS Research Centre within the Euromar Mermaid project. The sampler permits remote-controlled and event-controlled collection of water samples and performs a separation of the dissolved and the particulate phases immediately after sampling. Twenty-four water samples can be collected and assigned to events such as time, tide, current or turbidity. Samples are filtered directly after sampling through 0.40 μm polycarbonate filters and stored for further analysis. Tests on functionality, modifications of material and improvements in performance were carried out in the laboratory. Additional effort was exerted to achieve contamination-free samples and to extend the deployment time of the system. Determination of Cd, Cr, Cu, Fe, Mn, Pb and Hg in suspended matter was performed by atomic absorption spectrometry (AAS), total-reflection X-ray fluorescence spectrometry (TXRF) and inductively coupled plasma–mass spectrometry (ICP–MS) after digestion with nitric acid. Cd, Pb and Cu in the water column were analysed by anodic stripping voltammetry (ASV). Samples collected with a GoFlo water sampler agreed well with samples taken by the AISIT system even at ultra-trace levels in the open sea. The AISIT sampler allows effective and systematic research on the behaviour and the transport of trace metals. Daily sampling in the Elbe estuary during a high freshwater discharge event demonstrated the importance of an adaptive sampling strategy to investigate the transport of the trace elements from the Elbe River into the North Sea. Measurements directly after a high freshwater event showed that particle-bound metals were effectively transported into the coastal zone.