Extraction of arsenic-containing anions by supercritical CO2 with ion-pairing

The extraction of arsenic-containing anions from solid matrices by supercritical CO2 (sc-CO2) extraction coupled with ion-pairing was investigated. Tetra-butylammonium bromide (Bu4NBr), tetra-hexylammonium bromide (Hex4NBr), tetra-octylammonium bromide (Oct4NBr), dodecyltrimethylammonium bromide (Dod(Me)3NBr), myristyltrimethylammonim bromide (Myr(Me)3NBr) and hexadecyltrimethylammonium bromide (Hex(Me)3NBr) were used as the ion-pairing reagents. A model of the extraction of the arsenic-containing anions by supercritical CO2 extraction with pre-ion-pairing was proposed, and verified with experimental results. The extraction efficiency depends on two parameters, which are the theoretical extraction efficiency (Emax) and the rate constant (k). The effects of the molecular structure and size of the ion-pair reagent on Emax and k were discussed. The process parameter effects on the extraction efficiency, including the temperature, pressure, the mole flow rate of CO2, the mole ratio of alcohol to CO2 and the dosage of the ion-pair reagent were investigated using But4NBr and Myr(Me)3NBr as the ion-pairing reagents.