Abstract: An electrode assembly for use in quantifying the levels of various metals in an aqueous solution. In one embodiment, the electrode assembly comprises a substrate, the substrate being a silicon chip upon which a layer of silicon dioxide has been grown. A plurality of gold bond pads and gold interconnect traces are deposited by microphotolithography onto the silicon dioxide layer. An array of iridium deposits are then patterned by microphotolithography onto the interconnect traces at predefined locations. A passivation layer is deposited by plasma enhanced chemical vapor deposition over the finished metallization to electrically insulate it from external solutions. Plasma etching is then used to expose at least a portion of each of the iridium deposits. Just prior to analytical use, one or more of the exposed iridium elements are electroplated with mercury. The present invention is also directed to a field deployable sensor including the above-described electrode assembly.