Using a continuous flow apparatus, extraction of maleic acid and phthalic acid from their mixture by supercritical carbon dioxide saturated with trioctylamine (scCO(2)-TOA), have been performed at temperatures of 308, 318, and 328 K and in the pressure range of (100-350) bar and flow rate of 0.2 mL min(-1) of liquid CO2. Since the acids are polar compounds and can hardly be extracted by scCO(2), trioctylamine as an ion-pair forming reagent was used to increase the extraction yield of the acids. The amount of extraction of maleic acid and phthalic acid increased with pressure up to 250 and 200 bar, respectively, where it reaches a plateau at different temperatures. The amount of extracted maleic acid by scCO(2)-TOA was higher than the amount of extracted phthalic acid and it was much higher than the solubility of them in neat scCO(2). The amount of the acids extracted was also increased with increasing temperature. Moreover, the extraction selectivity of maleic acid to phthalic acid (alpha = y(1)/y(2)) of 7.7 was achieved at 318 K and pressure of 250 bar. The method was established as a selective and green extraction method for dicarboxylic acids such as maleic and phthalic acids. (c) 2008 Elsevier B.V. All rights reserved.