Capillary electrophoresis (CE) continues to grow rapidly as an analytical technique in a wide range of application areas (1-5). Typically, CE separations are performed in fusedsilica capillaries with internal diameters of 25-100 pm. High heat dissipation efficiencies in the narrow columns allow separations to be performed at high field strengths (200-500 V/cm), resulting in short analysis times and peak efficiencies of up to millions of theoretical plates.

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Absorbance detection in capillary electrophoresis (CE) offers excellent mass sensitivity but relatively poor concentration sensitivity. This dichotomy arises from the short optical path lengths found in current detector designs. Minimum detectable concentrations range from 10-5 to 10-7 M. The theoretical and physical design aspects affecting signal, noise, and optical transmission of various commercial (CE) detector cells are discussed. A new Z-shaped cell is described which uses a quartz ball lens to optimize light throughput in a 3-mm capillary section. The optical enhancement of the cell provides more than 1 order of magnitude improvement in the signal-to-noise ratio (MDC to 10-8 M) over that of a conventional cell design with sapphire ball optics. The effect of the increase in cell path length and volume is evaluated for electrophoretic efficiency and resolution. For peak efficiencies up to 200 000 plates, extention of overall path length from 0.075 to 3 mm results in less than 14% loss in efficiency. The new cell design also provides an improvement of linear dynamic range from ~3.5 orders of magnitude with a conventional cell to more than 4 orders of magnitude.

The clearance and organ distribution of virulent Nocardia asteroides GUH-2P and the avirulent mutant GUH-2AI at different stages of growth was determined after intravenous inoculation into BALB/c mice. The mutant differed significantly from the parent strain in its ability to survive and grow within the murine host.Since the mutant GUH-2AI had a very different colonial morphology compared with GUH-2P, it was believed that cell surface components might be affected by the mutation that resulted in the loss of virulence. Therefore, cell walls of both GUH-2P and GUH-2AI at different stages of growth were prepared and their composition determined. There were growth-stage-dependent changes in the composition of the cell walls that appeared to correlate with concurrent alterations in virulence; however, the overall chemical composition of the cell wall of the mutant (GUH-2AI) was not significantly different from that of the parent strain (GUH-2P). Both strains demonstrated significant modifications in fatty and mycolic acid composition at different stages of growth.Furthermore, the specific composition of C. mycolic acids was very different in virulent log-phase cells compared with less-virulent stationary-phase cells, and the avirulent mutant lacked a CS4:3 mycolate that was prominent in the virulent log-phase GUH-2P. Thus, CS4:3 mycolic acid represented 2.5% of the cell wall (dry weight) in log-phase GUH-2P, but it was undetectable in the walls of GUH-2AI at the stationary phase of growth. These results suggest that certain mycolic acids are associated with virulence.

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