A PDMS sheath flow cuvette for high-sensitivity LIF measurements in CE

A simple method for producing a sheath flow cuvette in PDMS suitable for post-column detection in CE is described. Two types of cuvette were investigated. In the first, the sheath flow channel had a round cross-section of approximately 635 microm diameter, whereas the second cuvette had a 300x300 microm(2) square channel. Both cuvettes produced laminar flows that ensheathed the separation capillary's effluent allowing sensitive fluorescence measurements. The elasticity of the PDMS allowed the 300x300 microm(2) square sheath flow channel to expand uniformly and accommodate the larger 330-340 microm od round separation capillary, producing a self-aligning cuvette with robust mechanical properties. With this cuvette, linear calibrations of over five orders of magnitude and 15-30 zmol fluorescein detection limits were obtained for 12 and 50 microm id capillaries.