Unclassified13. ABSTRACT 'Mavir'um 2?0 worasj By carefully controlling the copolymerization of phenol and 2-allylphenol onto the outsides of flame etched carbon fibers, a method to construct voltammetric probes with overall physical dimensions as small as 400 nm has been developed. The primary factors controlling the formation of a thin, yet insulating film are relative monomer concentration, polymer electrodeposition time, and electrodeposition solution pH. Optimal conditions for this procedure involve electrodeposition for 12 to 14 min in 60 mM phenol and 90 mM 2-allylphenol (pH = 9.0). Success rates for construction of electrodes with total structural tip diameters below 1.5 .m is approximately 70%, and for construction of electrodes with approximately 400 nm tip diameters it is about 10%. 14. SUBJECT TERMS 15. NUMBER OF PAGES submicron carbon electrodes, flame etched carbon fibers, 35 16. PRICE CODE 17. SECURITY CLASSIFICATION Id. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION

Bile salt micelles can be employed as a pseudo-stationary phase in micellar electrokinetic capillary (MEKC) separations of chiral analytes. To improve MEKC separations of chiral analytes, a molecular level understanding of micelle aggregation in the presence of analyte is needed. Here, aggregation of sodium cholate has been observed by exploiting the presence of a model analyte molecule. The 31 P and 1 H nuclear magnetic resonance spectroscopy (NMR) chemical shifts of (R,S) 1,1′-binaphthyl-2,2′-diylhydrogenphosphate (R,S-BNDHP), a model analyte in chiral MEKC separations, are demonstrated to be very sensitive to the aggregation state of the bile salt sodium cholate. In addition to probing micellar aggregation, the NMR spectral resolution of enantiomeric species is also strongly correlated with chiral separations in MEKC. In this work, the aggregation of sodium cholate in basic solutions (pH = 12) has been observed over the concentration range 0-100 mM. The primary cmc was found to be 14 ± 1 mM for basic solutions of sodium cholate. In addition a primitive aggregate is clearly observed to form at 7 ± 1 mM sodium cholate. The data also show pseudo-cmc behavior for secondary aggregation observed in the regime of 50-60 mM cholate. Finally, the H5-H7 edge of BNDHP is shown to be sensitive to chirally selective interactions with primary cholate micelles.

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Iontophoresis uses electricity to deliver solutes into living tissue. Often, iontophoretic ejections from micropipettes into brain tissue are confined to millisecond pulses for highly localized delivery, but longer pulses are common. As hippocampal tissue has a ζ-potential of approximately –22 mV, we hypothesized that, in the presence of the electric field resulting from the iontophoretic current, electroosmotic flow in the tissue would carry solutes considerably farther than diffusion alone. A steady state solution to this mass transport problem predicts a spherically symmetrical solute concentration profile with the characteristic distance of the profile depending on the ζ-potential of the medium, the current density at the tip, the tip size and the solute electrophoretic mobility and diffusion coefficient. Of course, the ζ-potential of the tissue is defined by immobilized components of the extracellular matrix as well as cell-surface functional groups. As such, it cannot be changed at will. Therefore, the effect of the ζ-potential of the porous medium on ejections is examined using poly(acrylamide-co-acrylic acid) hydrogels with various magnitudes of ζ-potential, including that similar to hippocampal brain tissue. We demonstrated that nearly neutral fluorescent dextran (3 and 70 kD) solute penetration distance in the hydrogels and OHSCs depends on the magnitude of the applied current, solute properties, and, in the case of the hydrogels, the ζ-potential of the matrix. Steady state solute ejection profiles can be predicted semi-quantitatively.

Carbon fiber microdisk electrodes ( 11 pm in diameter) were activated In sHu via intense laser pulses produced by a small nitrogen laser. The laser beam was focused down to a small spot size to ensure adequate power density. The laser treatment resulted in more Nernstlan voltammetry for dopamine, 4-methylcatechoi, and 3,4dIhydroxyphenylacetate In several different buffer systems over a range of pHs. The effect of buffer composition and pH on the apparent electrode kinetics observed both before and afler laser treatment was studied. An apparent cleaning of the electrode surface by the laser pulses resuits In more Nernstlan voltammetry; however, voltammograms obtained In some buffer systems, particularly those containing citrate, show anomalous effects afler laser treatment. A model of the activation process Is presented that might explain the observed phenomenon by surface ablation exposing clean, active carbon, followed by adsorption of solutlon species. This activation procedure is presented as a shnple, fairly inexpensive 'way to obtain consistent, repetitive voltammetry at carbon fiber microdisk electrodes.