This effort is directed toward the development of a multisensor device that is capable of characterizing the conductive and corrosive nature of a medium. More specifically, a device is being developed and tested with the intent of identifying electrolytes in both the aqueous and solid states, as well as to develop the methodology needed to analyze and interpret the data. Ultimately, the integration of the sensor into a subsurface explorer probe aims to determine the feasibility of (1) grounding experimental devices on Martian soil, (2) utilizing the soil as an electrical return path, and (3) using the experimental data to design materials that will prevent the corrosion of devices that come into contact with Martian soil. While the focus of the research centers upon the development of a device to study interplanetary surfaces, commercial applications are feasible and anticipated. These may include but are not limited to agricultural, biological, and geological analyses.

To accommodate these goals, a device was constructed that consists of three major components (figure 1). The first is an ion selective electrode (ISE) array, which has the potential of determining individual ions in solution based upon the potentiometric analysis across a carrier-based polymeric membrane. The second constituent of the device aims to complement the first technique by using anodic stripping voltammetry (ASV). ASV is an analytical method in which analytes are preconcentrated on the surface of a working electrode for a specific duration. Through an anodic potential scan, the analyte is then stripped from the working electrode and is oxidized back to its original form, with a voltammetric determination indicating the ions present in solution. The final element of the device consists of a galvanic cell array. Using this methodology, the galvanic couples are arrayed, and the current is measured between differing anodic and cathodic metals. While in contact with an electrolyte, the short-circuit current generated between the galvanic couples is then monitored. Through the use of pattern recognition techniques, an investigation will ensue to analyze the electrolyte present in solution. In essence, the galvanic cell array will then be used to determine the conductive and corrosive nature of the matrix in question.

Most beneficial to the development of the multisensor is the choice of differing methods of analysis. Specifically, while individual analytes may be difficult to discriminate using one technique, the multiple processes may allow for the determination of ionic species in a multicomponent solution at concentration limits unobtainable with any one technique by itself. In response to this need, a prototype device was built by the Jet Propulsion Laboratory (JPL) and delivered to KSC in December 2001. This prototype is shown in figure 2. In order to determine whether the complex device is working properly, a resistor card was employed to test and improve the device in the acquisition of data. Initial studies have centered upon the concentration dependent analysis of individual ions present in solution, with multianalyte determinations employed to represent real-world conditions.

Figure 1. Diagram of Sensor Based on Electrochemical Techniques To Detect and Identify Ions in Solution

Figure 2. Fluidics Board

Contact: Dr. L.M. Calle (Luz.Calle-1@ksc.nasa.gov), YA-C2-T, (321) 867-3278
Participating Organizations: NASA/JPL (Dr. M.G. Buehler), NASA/KSC (N.P. Zeitlin), Swales Aerospace (Dr. M.R. Kolody), and Tufts University (Dr. S.P. Kounaves)