Abstract: A method is provided for the integration of a low-volume liquid flow and ing system and a portable optical waveguide-based fluorescence detector for the chemical analysis of reagents in fluorescence-based reactions. The method is particularly applicable to the detection of enzyme inhibitors, modifiers, or ligands in cases where a fluorescent enzyme substrate or product exists. In a preferred embodiment, the presence and concentration of acetylcholinesterase inhibitors, such as chemical warfare nerve agents or certain insecticides, is determined by mixing aqueous samples with a dilute solution of n-methyl indoxyl acetate, and monitoring the formation of a fluorescent product (n-methyl indoxyl). The presence of an acetylcholinesterase inhibitor reduces the amount of fluorescent product formed in a given time period.