Abstract: A process for detecting the presence of trace amounts of non-fluorescent soluble compounds each having at least one labile hydrogen atom in a carrier solution by adding a non-fluorescent quinone which is reducible to a fluorescent hydroquinone, and irradiating the resulting solution in the absence of oxygen with light of sufficient energy to cause the quinone to be reduced to a hydroquinone. The invention further provides a novel photochemical reactor--recording fluorometer combination and carrier liquid--quinone solution for performing the analysis.