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The present paper describes the development of a new clean-up strategy for the analysis of aflatoxins (AFs) in food. The sample preparation method is based on immuno-ultrafiltration (IUF) which, in contrast to immunoaffinity chromatography, makes use of antibodies in free form. After selecting an appropriate ultrafiltration (UF) device and optimizing different operation conditions the IUF method was applied to the clean-up of maize and rice. Quantification of AFs was carried out by HPLC and fluorescence detection, after postcolumn derivatization in a Kobracell. The IUF method was shown to be as selective as sample clean-up using commercial immunoaffinity columns. Recovery rates and RSD for the AFs G(2), G(1), B(2) and B(1) in spiked rice were found to be 76 +/- 3, 76 +/- 2, 83 +/- 5 and 99 +/- 14%, respectively. The analysis of a FAPAS (food analysis performance assessment scheme) maize material resulted in AFs concentrations which were in the range assigned by the producer of the reference material.