A simple HPLC method has been developed for the determination of organic acids adsorbed on particles of maghemite. The advantage of this described technique is the possibility to identify and measure the ratios of differents acids bounded on the same particle. The chromatographic analysis is achieved on a sulphonated copolymer column in acidic form. Good recoveries of the acids were obtained by dosing the free acids in the supernatant and the acids adsorbed on the particles.