Metals and other chemicals in marine waters and sediments can be measured in situ at concentrations as low as one part per billion, thanks to a new microelectrode developed by Delaware Sea Grant researcher George Luther and his colleagues. Until now, sensors could characterize only gaseous compounds, and typically only one gas could be measured per electrode. The new microelectrode consists of a gold wire plated with mercury and enclosed in a glass tube. The mercury in the wire reacts with chemicals, each having a different peak potential, in marine water or sediment. The reaction creates a current directly proportional to the chemical's concentration. The design overcomes the problems of existing electrodes, which survive poorly in the muddy marine field conditions.