There are different types of optical capillary cells in use for the modern on-line UV-VIS analysis of liquids using fibre spectrometers. These cells have the advantages of low sample volume, long optical pathlengths and compatibility to fibre optics. In this paper, we will show that the liquid core waveguide (LCW) is a particularly useful device because the light intensity is confined in the liquid core. This is shown in two ways. Firstly, the measured total optical losses of the LCW capillary device indicate typical guiding losses less than 3 dB m-1 without a significant dependence on either fibre diameter or on the diameter of the capillary. Secondly, measurements of the radial intensity distribution exhibit a clear maximum in the core in the case of the LCW device. The efficiency of a liquid core waveguiding cell is investigated for different core diameters (0.3-4 mm) in combination with different coupling fibre diameters (200-600 µm). A thin cell with a 360 µm diameter with a sample volume in the µl range and low coupling losses will be discussed as well.

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