The factors that affect the sensitivity enhancement in luminescence measurements acquired with capillary/fiber optical sensors (C/FOS) versus conventional sensors without the capillary were investigated. A model in which the capillary acts as a partially reflective waveguide was devised and tested. This model takes into account the optical properties of the sample, capillary, and surrounding medium.;The dependence of the enhancement on the capillary length and sample solution concentration predicted by the model were compared to experimental fluorescence data obtained with non-absorbing and absorbing quartz capillaries, and with metallic capillaries. The greater enhancements (about 80) were observed for the non-absorbing capillaries. A five-fold reduction in enhancement was observed when water instead of air surrounded the C/FOS.;The applicability of these C/FOS to the collection of Raman scattering and chemiluminescence signals was demonstrated. Besides sample volume reduction, significant improvements in sensitivity and detectability were achieved compared to the conventional sensors.
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