Dennis C. Shelly

Study of the effect of sliding velocity on the frictional properties of nonwoven fabric substrates

Frictional properties of nonwoven substrates have been investigated using a sliding friction apparatus. Nonwoven substrates were developed using a modern needle-punching nonwoven technology. The experiment was conducted over a range of applied normal loads. The study was aimed at understanding the effect of testing speeds on the frictional properties of needle-punched nonwoven substrates. Frictional properties were characterized using friction factors, C, n and R. Results indicate that as the speed of the testing increased, frictional resistance increased.

Optical properties of axial-illumination flow cells for simultaneous absorbance-fluorescence detection in micro liquid chromatography

Abstract Simultaneous measurements of absorbance and fluorescence are possible with axial-illuminated flow cells, fashioned with a unique bend geometry. The optical properties of these flow cells have been studied. Effects of variations in lumen refractive index, capillary wall thickness and physical pathlength have been examined. A theoretical understanding of the various light propagation modes and of light intensity distributions in these modes, based upon lumen refractive index, has been attained. Of more practical significance, optical pathlengths from

Simultaneous absorbance, fluorescence and refractive index (SAFRIN) detection for Micro LC

Abstract Absorbance, fluorescence and refractive index detection are simultaneously accomplished in a Micro LC system. A unique double eccentric-bend fused silica capillary is employed with axial illumination to achieve a long path length, multisensing flow cell. Two different optical sources, one that excites fluorescence through absorption and one that is not absorbed by eluting analytes, are imaged into the bends with optical fibers, placed within the capillary lumen in separate legs of the device. Axially-propagating light exits at each bend where photodetectors simultaneously collect attenuated light, one signal based on absorption and the other signal based on refractive index. A nearby cylindrical lens, optical filter and photomultiplier tube collect fluorescence in the ‘absorption’ leg of the capillary. Thus, trifunctional detection is achieved in microscale liquid chromatography.

Axial illumination of fused-silica capillaries: Investigation of fluorescence and refractive index detection

Abstract The optical waveguide properties of fused-silica capillaries enable greater illuminated sample volume by axial illumination, as compared to cross capillary illumination. Several modes of light propagation inside these unique optical waveguides are described. A micro-LC flow cell featuring axial illumination with mobile phase elimination by nebulization has been developed and evaluated. This device was used in the construction and evaluation of laser-induced fluorescence and laser-based refractive index detectors. A summary of results from our studies and a survey of the various detection possibilities, theoretically compatible with axial illumination of capillary waveguides, are presented.

Amperostatic-potentiometric detection for micro high-performance liquid chromatography

Abstract Constant current is applied to a microelectrode which is “bathed” in the effluent from a micro-LC column. A micro indicator electrode senses the potential as electroactive solutes undergo electron transfer at the working electrode surface. In the absence of analyte, mobile phase components (principally water) are reduced or oxidized, generating a significant working electrode potential. Because the measured signal (potential or charge density) is significant near the detection limit, detection sensitivity may, under optimum conditions, be higher than for conventional amperometric detection. We report on the design, fabrication and evaluation of amperostatic-potentiometric (ASPEN) detection for micro-LC. The determination of phenol, o -chlorophenol, 2,4-dimethylphenol and p -benzylphenol, each at the femtomole level (injected amount), has been performed with a packed fused-silica capillary (250 μm I.D.), operating in the reversed-phase mode. The real and apparent limitations to this technique will be presented.