A new method for the removal of the arsenic in the form of anions such as arsenite and arsenate, from solid samples by supercritical CO2 extraction coupled with ion pairing was investigated. Tetrabutylammonium bromide (Bu4NBr) was used as the ion-pairing reagent. As a result of the insolubility of Bu4NBr in supercritical CO2, the extraction of the anions by supercritical CO2 with the in situ ion-pairing is not effective. The arsenic in the form of anions in the solid samples can be effectively removed by supercritical CO2 extraction with pre-ion-pairing. For the case of the pre-ion-pairing, the extraction efficiency was strongly dependent on the dosage of Bu4NBr. (C) 2002 Elsevier Science B.V. All rights reserved.