Abstract The cyclic condensation of malonic acid with acetic anhydride in non-aqueous media is catalyzed selectively by tertiary amines. This derivatization reaction is adapted for flow injection analysis. A reaction pathway for the cyclization of a mixed anhydride condensate to form a fluorescent fully acylated phloroglucinol carboxylic acid is proposed. The effects of reaction parameters on the sensitivity of the reactionare described and calibration data are presented for ⩽2.7 mM triethylamine, tripentylamine, N,N-diethylaniline and pyridine. A secondary amine (diethylamine) gave a negligible response, but both primary and secondary amines partially quenched the fluorescence induced by a tertiary amine.