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Comparison of sensors for trace metals in natural freshwaters

Results are presented of application of several sensors for trace metal speciation analysis in freshwater systems. All techniques were used simultaneously during a multi-partner field campaign. The techniques are compared with respect to their performance and to the metal species concentrations (Cu, Zn, Cd and Pb) detected.

The analytical sensors comprise:

- Diffusion gradients through thin-film gels (DGT);
- In situ voltammetry using gel-impregnated microelectrodes (GIME-VIP, Gel Impregnated Microelectrode Voltammetric In situ Profiling system);
- Stripping chronopotentiometry (SCP);
- Permeation liquid membranes (PLM);
- Donnan membrane technique (DMT);
- Competitive ligand-exchange / stripping voltammetry or adsorption stripping voltammetry (CLE-SV or CLE-AdSV).

All methods were found to be applicable in both hard-waters and soft-waters, although in some cases problems with detection limits were encountered at the low total concentrations in pristine waters. The detected Cu, Cd and Pb concentrations decreased in the order DGT > GIME-VIP > PLM > DMT, in agreement with the theoretical expectations.

Methods involving in situ measurements (GIME-VIP) or in situ exposure (DGT, DMT and PLM) appear to be appropriate in avoiding artifacts of sampling and sample handling. This result will be submitted for publication in the international peer reviewed journal, Environmental Science & Technology. It is useful for any end user that is concerned with measurement of trace metals in freshwaters, e.g. other researchers, water-monitoring agencies.

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