Extended path length UV absorbance detector for capillary zone electrophoresis

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Abstract
A method of UV absorbance detection for use in capillaries using axial as opposed to transcolumn illumination is described in which laser‐induced fluorescence acts as a tool for determining, indirectly, the absorbance within a given length of the capillary. The length of the optical path can be chosen arbitrarily, regardless of the capillary diameter. The technique is demonstrated by means of capillary zone electrophoresis (CZE), in which path lengths of up to a few millimeters can be tolerated without serious loss of separation efficiency. Results for 50‐μm‐diameter capillaries show that optical densities consistent with an optical path of 3 mm can be obtained. This leads to a considerable increase in absorbance signal, compared with the usual transcolumn UV absorption technique. It is concluded that further exploitation of the technique requires the use of a more stable light source.