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The packing of submicrometer sized silica beads inside a microchannel was enabled by a novel method which avoids the complication and limitations of generating a frit using conventional approaches and the restriction of flow using a submicrometer sized weir. A micrometer sized weir and two short columns of 5 m and 800nm silica beads packed in succession behind the weir together functioned as a high pressure frit to allow the construction of a primary packed bed of 390nm silica beads. This packed bed microchannel was tested as an EOF pump, wherein it exhibited superior performance with regards to pressure tolerance, i.e., sustaining good flow rate under extremely high back pressure, and maximal pressure generation. Under a modest applied electric field strength of 150 V/cm, the flow rate against a back pressure of 1200 psi (~8.3 MPa) was 40 nL/min, and the maximal pressure reached 1470 psi (~10 MPa). This work has demonstrated that it is possible to create a high performance packed bed microchannel EOF pump using nanometer sized silica beads, as long as proper care is taken during the packing process to minimize the undesirable mixing of two different sized particles at the boundaries between particle segments and to maximize the packing density throughout the entire packed bed., Published in the Journal of Chromatography A, v1217 p7153-7157, 2010.

Practical considerations for the injection and separation of nitroaromatic explosives in seawater sample matrices are discussed. The use of high surfactant concentrations and long electrokinetic injections allows for improved detection limits. Sensitivity was enhanced by two mechanisms, improved stacking at the detector-side of the sample plug and desorption of analyte from the capillary wall by surfactant containing BGE from the inlet side of the sample plug. Calculated limits of detection (S/N = 3) for analytes prepared in pure seawater were 70-800 ppb with injection times varying from 5 to 100 s., Published in Jnl. of Chromatography A, p1-7, 2010.

Final report detailing effort to develop a capillary electrophoresis (CE) microchip sensor for the real-time, sensitive and selective detection of energetic explosives in seawater. Two primary issues are specifically addressed: 1) the development of new methods for enhancing the sensitivity to explosives via a pre-concentration step from seawater into the nonaqueous solvent, acetonitrile, and subsequent electrochemical detection following their microseparation on a microchip; and 2) methods for increasing the speed of analysis by employing the ultra-miniaturized solid phase extraction step that is coupled to a high speed microchip separation platform.

The closure and remediation of former ammunition plants and military facilities requires accurate characterization of soil and groundwater contamination. Some of the pollutants found at these facilities are nitroaromatic and nitramine explosives and their biological and photolytic degradation products [1]. It has been found that the distribution of contamination is often highly heterogeneous, requiring numerous samples and analyses for these sites to be adequately characterized [1]. A number of different methods have been applied to the analysis of explosives, including gas [2], liquid [3-5], thin-layer chromatographies [6], Raman spectroscopy [7], electrochemical sensor [8], and immunoassay techniques [9]. It would be highly advantageous to develop a field analyzer capable of reliable and cost-effective analysis of explosives in environmental samples. Groundwater in contaminated sites usually contains several related compounds and their degradation products: 14 compounds in the U.S. Environmental Protection Agency (EPA) 8330 method. Therefore, simultaneous detection of these explosives in complex environmental matrixes by Raman spectroscopy, immunochemical sensors, or electrochemical sensors would be difficult and requires a chromatographic separation technique. The EPA specifies SW-846 Method 8330 for the trace analysis of explosive residues in water, soil, or sediment matrixes [10]. Following sonication, extraction with acetonitrile, and preconcentration, analysis for 14 species is performed using high-performance liquid chromatography (HPLC) and ultraviolet (UV) absorption. Isocratic HPLC separations using commercially available C18 columns typically take over 30 minutes and are unable to separate the two aminodinitrotoluene isomers and two of the three dinitrotoluene isomers [11]. To fully identify each of the 14 compounds, an additional HPLC run must be performed using a cyano column, leading to an increase in analysis time and sample handling complexity., Prepared in collaboration with Pacific Northwest National Laboratory, Richland, WA, and the Dept of Chemistry and Biochemistry, New Mexico State University, Las Cruces.

A simple, semi-automated, microcolumn solid-phase extraction (SPE) system is optimized for the extraction, preconcentration and HPLC analysis of seven different explosives and explosive derivatives contaminating seawater, river water and well water samples. The microcolumns were constructed from 1/16 in. O.D. PTFE tubing (1 in. =2.54 cm) packed with 0.5-1.5 mg of SPE material, LiChrolut EN or Porapak R. The extraction system consisted of two syringe pumps and several solenoid valves. Optimal detection limits were realized when the sample water flow-rate was maximally increased within the limits of the pump, 5-10 ml/min (despite exceeding the breakthrough threshold of the SPE microcolumn), and when the eluate volume collected from the column was minimized, <5 mul (despite very low recovery percentages)., Pub. in Jnl. of Chromatography A, v991 p159-167, 2003.