1,1,1-Trifluoromethanesulfonic Acid 2-(1,3-Dihydro-1,3-dioxo-2H-benz[f]isoindol-2-yl)ethyl Ester is used as a reactive ultraviolet and fluorescent labeling agent for determining the presence of carboxylic acids by high performance liquid chromatography. 1,1,1-Trifluoromethanesulfonic Acid 2-(1,3-Dihydro-1,3-dioxo-2H-benz[f]isoindol-2-yl)ethyl Ester is also used as a derivatization agent.