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 μm diameter, whereas the second cuvette had a 300x300 μm² 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 μm² square sheath flow channel to expand uniformly and accommodate the larger 330-340 μm 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 μm id capillaries.