Patent ID: 7498402

Claim:
A method of purifying a treatment target substance containing a fluorine-containing surfactant and water which comprises removing at least part of the fluorine-containing surfactant from said treatment target substance by contacting said treatment target substance with a substance B comprising carbon dioxide, wherein said substance B is a gas under standard conditions (10 5 Pa, 0° C.), said fluorine-containing surfactant is an ether oxygen-free anionic compound represented by the general formula (1): Y—(CF 2 ) x1 —(CH 2 ) y1 -A (1) wherein Y represents H or F, x1 represents an integer of 4 to 13, y1 represents an integer of 0 to 3 and A represents —SO 3 M or —COOM (in which M represents H, NH 4 , Li, Na or K), or an ether oxygen-containing anionic compound represented by the general formula (2): F(CF 2 ) x2 O(CFXCF 2 O) y2 —CFX-A (2) wherein x2 represents an integer of 1 to 5, y2 represents an integer of 0 to 10, X represents F or CF 3 and A represents —SO 3 M or —COOM (in which M represents H, NH 4 , Li, Na or K).