In order to have as simple a chromatographic setup as possible, laser-based forward scattering degenerate four-wave m ixing (F-D4WM) detection is applied directly to fused-silica capillary¯ow cells that can be used in micro-column liquid chrom atography (m LC). Compared to the previously used specially designed¯ow cells (optimized from an optical point of view), such cylindrically shaped cells have obvious disadvantages such as background scatter and signal beam distortion. H owever, a laser beam can be focused easily in a fused-silica capillary, yielding a laser-probed volume of less than 100 pL, which is attractive for miniaturized chrom atographic system s. Parameters such as capillary dimensions (internal and outer diameters), capillary con® guration in relation to eluent ow direction,¯ow rate, and various background suppression techniques are considered from a theoretical and a practical point of view and subsequently optimized. Interestin gly, the direction of the eluent¯ow is critical; it should be in the plane formed by the two laser beams. m LC/F-D4WM is used to analyze spiked river Rhine water.
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