Quantification of desferrioxamine, ferrioxamine and aluminoxamine by post-column derivatization high-performance liquid chromatography - Non-linear calibration resulting from second-order reaction kinetics

Desferrioxamine B is widely used as therapeutic agent for removal of excess body iron and, more recently, for removal of aluminium. A HPLC-based method for direct sensitive and reliable determination of ferrioxamine, desferrioxamine, aluminoxamine and related metabolites has been developed for use in pharmacokinetic studies. The method consists of complete separation of the analytes by an optimized mobile phase avoiding conversion of desferrioxamine to ferrioxamine by the analytical system and overcoming problems due to peak tailing properties of desferrioxamine. A post-column derivatization reaction with colourless fluoro-complexed iron converts all iron free species to ferrioxamine and allows quantification at 430 nm avoiding interference of UV-absorbing coelutes. This reaction might be of interest for other analytical procedures concerning iron chelators. The influence of the post-column reaction system on the column plate number is characterized. As the reaction rate of desferrioxamine and aluminoxamine with iron(III) is of second-order kinetics, a quadratic calibration function is observed, resulting from a compromise between residence time and peak broadening. A solid-phase extraction procedure is presented for extraction of the analytes from plasma. Limits of detection (SIN ratio of 3) were determined as 1.95 ng for ferrioxamine, 3.9 ng for aluminoxamine and 15.7 ng for desferrioxamine, expressed as on-column load. A new iron-free metabolite was identified with fast atom bombardment-mass spectrometry as N-hydroxylated desferrioxamine. (C) 1998 Elsevier Science B.V. All rights reserved.