Gabriela S. Chirica
Sandia National Laboratories
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Featured researches published by Gabriela S. Chirica.
Electrophoresis | 1999
Gabriela S. Chirica; Vincent T. Remcho
Designed especially for capillary electrochromatography (CEC), silicate‐entrapped columns are made by trapping particles of chromatographic packing material in a network of silica. Once entrapped, the capillary no longer requires frits. This renders a more homogeneous and stable packed bed. Accidental breakage of the fragile frits is not an issue with these robust columns. Columns packed with reverse‐phase material subjected to silicate entrapment demonstrated faster separations of retained analytes and increased efficiencies compared with nonentrapped columns. The method was also used to prepare chiral CEC columns by entrapping a molecular imprinted polymeric (MIP) packing having minimal surface charge density, thus being unable alone to support sufficient electroosmotic flow for CEC.
Journal of Chromatography A | 2001
Gabriela S. Chirica; Vincent T. Remcho
A new type of monolithic stationary phase was prepared within the confines of fused-silica tubing by in situ polymerization of divinylbenzene or ethylene dimethacrylate either with styrene or butyl methacrylate. The porosity of the monolith was dictated by silica beads packed in the capillary prior to flushing the column with the monomeric solution. Subsequent washing of the polymeric rod with sodium hydroxide rendered a porous monolith that was used for both micro-LC and capillary electrochromatography. The novelty of the approach presented herein lies in preparing the polymer within the confines of a fused-silica capillary. The challenges posed in this new context and their resolution are presented in detail. In addition, this study proposes that in addition to tailoring the pore size, the silica beads, through their surface chemistry, can influence the surface characteristics of the finished polymer monolith. For example, the data suggests that octadecyl modified silica particles interacted with hydrophobic moieties of monomers before initiation of polymerization, thus dictating their orientation in the resulting polymer.
Sensors and Actuators B-chemical | 2003
David S. Reichmuth; Gabriela S. Chirica; Brian J. Kirby
A zwitterionic additive is used to improve the performance of electrokinetic micropumps (EK pumps), which use voltage applied across a porous matrix to generate electroosmotic pressure and flow in microfluidic systems. Modeling of EK pump systems predicts that the additive, trimethylammoniopropane sulfonate (TMAPS), will result in up to a 3.3-fold increase in pumping efficiency and up to a 2.5-fold increase in the generated pressure. These predictive relations compare well with experimental results for flow, pressure and efficiency. With these improvements, pressures up to 156 kPa/V (22 psi/V) and efficiency up to 5.6% are demonstrated. Similar improvements can be expected from a wide range of zwitterionic species that exhibit large dipole moments and positive linear dielectric increments. These improvements lead to a reduction in voltage and power requirements and will facilitate miniaturization of micro-total-analysis systems (μTAS) and microfluidically driven actuators.
Electrophoresis | 2000
Gabriela S. Chirica; Vincent T. Remcho
A rapid and direct method for immobilizing conventional high performance liquid chromatography (HPLC) packing material inside fritless capillaries has been developed. Due to the simple composition of the entrapment matrix (tetraethoxysilane, alkyltriet‐hoxysilane, ethanol and water), straightforward manufacturing procedure and modest equipment requirement, the method can readily be transferred to any laboratory and easily automated. The entrapment procedure has minimal influence on the structure and chromatographic properties of the original reverse‐phase sorbent. Various immobilization solutions have been tested, and a comparison between columns entrapped with different immobilization mixtures and conventional packed capillaries is presented. High effficiency separations were obtained using tert‐butyl‐triethoxysilane entrapped columns in both capillary electrochromatography (reduced plate heights of 1.1—1.4 were measured) and microliquid chromatography (reduced plate heights of 2.2—2.6 were observed) formats. Elimination of frits, stabilization of the packed bed and on‐the‐fly customization of column length render mechanically robust columns that are remarkably stable over time, from which manufacturing imperfections can be removed easily.
Journal of Separation Science | 2002
Angela Doneanu; Gabriela S. Chirica; Vincent T. Remcho
Methacrylate-Based monolithic capillary columns for liquid chromatography and capillary electrochromatography were prepared within the confines of fused-silica tubing using Starburst (PAMAM) dendrimers to affect porosity. Different column porosities were obtained by varying the amount of the dendrimer template as evidenced by electron microscopy. Mercury intrusion porosimetry measurements provided additional information. The effect of dendrimer concentration on chromatographic performance was studied in detail.
Journal of Chromatography B | 2011
Geun-Cheol Gil; Jim Brennan; Dan Throckmorton; Steven S. Branda; Gabriela S. Chirica
We demonstrate use of restricted access media with reversed phase functionality (RAM-RP) for analysis of low molecular weight proteins and peptides in mouse serum (75 μl) using a custom designed modular automated processing system (MAPS). RAM-RP fractionation with simultaneous removal of high molecular weight and high abundance proteins is integrated with a follow-on buffer exchange module (BE) to ensure compatibility with subsequent processing steps (trypsin digestion and intact peptide separation prior to mass spectrometric analysis). The high sample capacity afforded by chromatographic methods generates enough sample to achieve comprehensive serum peptidome identification (357 proteins) through tandem mass spectrometric analysis of both intact and digested peptides. Sample losses during transfer between modules are minimized through precise fluidic control; no clogging occurred over several months of serum processing in our low back pressure system. Computer controlled operation of both modules and thorough optimization yield excellent run-to-run reproducibility and protein/peptide overlap in analytical repeats. The robustness of our results demonstrate that the RAM-RP-BE workflow executed on our MAPS platform shows tremendous potential for high throughput peptidome processing, particularly with regard to direct analysis of small-volume serum samples.
Analytical Chemistry | 2000
Gabriela S. Chirica; Vincent T. Remcho
Microbial Pathogenesis | 2006
Rajat Sapra; Sara P. Gaucher; J.S. Lachmann; G.M. Buffleben; Gabriela S. Chirica; Jason E. Comer; Johnny W. Peterson; Ashok K. Chopra; A.K. Singh
Archive | 2005
Gabriela S. Chirica; Ronald F. Renzi; Blake A. Simmons
Archive | 2008
Gabriela S. Chirica; Gregory J. Fiechtner; Anup K. Singh