There are more than 12,000 sites in the United States that are contaminated with one or more compounds related to weapons technologies. These sites include former and current testing and training facilities where waste from weapons manufacture, storage, and reclamation processes has leached into the soil and groundwater. Key contaminants include energetic compounds such as TNT, RDX, and HMX; perchlorate propellants; and degradation products of these contaminants. Many of these compounds are known carcinogens or suspected cancer causing agents. One issue has been the potential health hazard posed to military personnel and their families resident on these installations, but the migration and leaching of these contaminants to the surrounding population, agricultural regions, and neighboring wildlife is also a concern. Long-term monitoring of sites undergoing remediation as well as sites that may eventually require cleanup is critical. This project sought to develop materials, systems, and methods necessary to monitoring contaminants in surface and ground water through the use of target preconcentration prior to analysis by commercially available sensors.
Periodic mesoporous organosilicates (PMOs) are organic-inorganic polymers with highly ordered pore networks and large internal surface areas. They are synthesized using a surfactant template approach in combination with a phase separation technique to provide organization on both the macro- and meso-scales. This approach facilitates diffusion of targets throughout the entire available surface area. Using a template-directed molecular imprinting approach, a PMO surface can be engineered to have both a large adsorption capacity and selectivity for the target. The binding affinity and capacity of these materials make it possible to concentrate trace levels of targets from a large sample volume while eliminating other contaminants. The targets can be subsequently eluted from the sorbent in a small volume of solvent such as methanol or acetonitrile. This adsorption/elution approach is directly applicable to the development of methods and systems for use with electrochemical detection. Methods for utilization of these types of materials in the preparation of samples for ion mobility spectroscopy (IMS)-based detection were less well developed. This application involves sampling from a water source and desorbing the concentrated target into a carrier gas.
This effort sought both to advance the state of the sorbent materials and to provide the methods and systems necessary for their use in in-line preconcentration of targets. Several advances in sorbent design were made including improvements in morphological character and in the template used. Production of the materials at larger scale was also demonstrated. The PMO materials were shown to enhance the sensitivity of currently available sensor systems by concentrating trace amounts of nitroenergetic targets from large sample volumes. Materials for the preconcentration of perchlorates were also developed. A breadboard level prototype was developed and used in a full range of laboratory demonstrations with electrochemical sensing. A brassboard level prototype was developed and used for one round of field trials with electrochemical sensing. A breadboard level prototype was also developed for use with a commercial IMS detection system.
The novel porous materials and associated methods developed provide a regenerable mechanism for the preconcentration and long-term monitoring of energetic materials. Though development of the systems is not ongoing, the materials developed are being utilized by another group in the design of an electrochemical sensor for use with the REMUS (Remote Environmental Monitoring Units) Unmanned Undersea Vehicle. In addition to these types of active monitoring applications, the material developed has the potential for deployment for short- and long-term passive monitoring similar to the polyethylene passive sampling materials.