The remediation and closure of military facilities requires accurate characterization of soil and groundwater contamination. Contaminants at these facilities include nitroaromatic and nitramine explosives and their biological and photolytic degradation products. Contaminant distribution is often highly heterogeneous, requiring numerous samples and analyses for adequate characterization.  A number of different methods have been applied to the analysis of explosives—gas, liquid, and thin-layer chromatographies, Raman spectroscopy, electrochemical sensors, and immunoassay techniques. Simultaneous detection of these explosives-related compounds and their degradation products in complex environmental matrices by Raman spectroscopy, immunochemical sensors, or electrochemical sensors is difficult and requires a chromatographic separation technique.

The objective of this SERDP Exploratory Development (SEED) project was to develop a prototype of a portable analytical system based on the on-line coupling of a miniaturized solid-phase extraction (SPE) device or on-chip integration of a micro-SPE with a microfabricated capillary electrophoresis (CE)/electrochemical detector (ECD) capable of fast preconcentration, separation, and detection of explosives and their degradation products in groundwater.

An SPE-CE system includes three parts: the SPE part, the CE part, and a specially designed interface. The SPE part provides efficient pre-treatment options and can be tailor-made for specific applications. The CE separation technique is characterized by its high resolution, short analysis time, and multiple analyte capability. In this project, the interface between the SPE system and the CE-on-chip was achieved by using an interface flow channel with a volume-flow resistance that is lower than that of the electrophoresis separation channel. An electrolyte stream carries a sample plug eluted from the mini-column toward the CE-on-chip. The dimension of the sample flow channel is designed to be larger than that of the separation channel. While the sample plug passes along the separation channel, a small fraction of the sample is electrokinetically introduced into the separation channel. This addresses the small injection volumes required for the CE system. Moreover, it permits multiple injections into the separation channels while continuously applying the high voltage between separation channels.

CE microchips were fabricated on both glass and polymer substrates and integrated with an ECD.  Separation and detection processes were optimized for rapid analysis of explosive mixtures (<2 minutes).  An SPE system was also developed for preconcentration of explosives in groundwater that provides a 100-200x analyte enhancement.  An interface device was fabricated for an automated on-line SPE/micro-chip CE system. Initial testing demonstrated excellent reproducibility. Developmental work was also initiated on in situ/on-chip micro-SPE methods.

Results support the further development of an integrated, automated, and compact analyzer for the reliable and cost-effective characterization of groundwater contamination. Although the target analytes in this project were explosives, the analyzer can be extended to other contaminants. Primary cost-saving benefits are based on minimizing routine sampling and analysis of groundwater samples.