The objective is to concentrate organic acid traces in water samples. The influence of several parameters and their interactions on the adsorption of organic acids on anion exchange resins was studied. A complete factorial design 2 4 was hence performed. The measured response corresponds to the maximal percolation volume and the studied parameters were the nature and the mass of the resin, the percolation flow-rate and the ionic strength of the analysed water. The results shown that the pe r- colation flow-rate is significant but not really important compared to the resin mass and to the nature of water. Indeed, the sa mple inorganic anions can compete with organic acids. This adsorption competition appears to be more important when a macropo- rous resin is used. A gel-type resin could be therefore better adapted to the extraction of organic acids in water samples.