Microelectrodes for in situ voltammetric determination of pollutants

The toxicity of sediments is often closely bound to the labile toxic elements contents. In porewaters, metal concentrations are generally measured after separation from the solid material by means of pressure or centrifugation. The recent developments of in situ metal measurements by microsensors do not require any pretreatment of the sediment and hence avoid some possible artefacts like oxygen penetration in anoxic sediment and/or temperature modification. Our work describes firstly the preparation of microelectrodes based on a thin solid Silver (diameter: 30 mum) or Iridium (diameter: 75 mum) wire, covered at the tip with a fine layer of mercury. Secondly, an analytical procedure (based on cathodic voltammetry) is presented to measure Mn(II), Fe(II) and S(-II) concentrations, which play a relevant role in the metal pollutant cycle in sediments. By anodic stripping voltammetry, such microsensors are able to detect trace heavy metals such as Cd(II) or Pb(II) at relatively low concentration levels (similar to 1 mug.dm(-3)) with 5 minutes accumulation time. Finally, the most important challenge is to install the microelectrodes in natural media and to follow up metal pollution over a long time period.