The relationship between sample depth and the corresponding fluorescence signal excited and collected with a single-fiber fluorometric optical sensor has been theoretically derived. The effective depth, zeff, is defined as the sample depth from which 90% of the total fluorescence signal originates. This parameter can be theoretically predicted as a function of the fiber radius, r0, the acceptance angle, α, and the sample absorbance. For solutions of negligible absorbance, the effective depth is zeff = 9r0 tan−1α. The theoretical expressions have been experimentally tested with the use of 100- and 200-μm-core fibers and Rhodamine 6G solutions of different absorbances.
