Aqueous two-phase system of cationic and anionic surfactant mixture and its application to the extraction of porphyrins and metalloporphyrins Aijun Tong a,* , Ying Wu b , Shida Tan a , Longdi Li a , Yoshifumi Akama c , Shigeyuki Tanaka c a Department of Chemistry, Tsinghua University, Beijing 100084, China b Department of Fundamental Science, Xinjiang Alaer Talimu Agriculture University, Xinjiang Alaer 843300, China c Department of Chemistry, Faculty of Science and Engineering, Meisei University, Hino, Tokyo 191, Japan Received 18 November 1997; received in revised form 5 March 1998; accepted 7 March 1998 Abstract Aqueous two-phase system is obtained when a cationic surfactant with bigger alkyl polar head groups such as dodecyltriethylammonium bromide (C 12 NE) is mixed with an anionic surfactant like sodium dodecyl sulfate (SDS) at certain surfactant concentrations and molar ratios. When C 12 NE is in excess, the top phase is opalescent and is a surfactant-rich micellar solution, while the bottom phase is transparent and is a dilute micellar solution. Such a new aqueous two-phase separation system is employed in extractive separation practice. Several dyes with different chemical structure like anthraquinone, methyl red and methylene blue partitioned in the two-phase system are investigated. Porphyrin compounds and metalloporphyrins, i.e., hematoporphyrin (hemato), uroporphyrin (uro), Cu-TPPS 4 (tetraphenylporphine tetrasulfonic acid), Zn-TPPS 4 , Cu-T-4(TAP)P (tetrakis(p-trimethylammoniophenyl) porphine), are also extracted with the present two-phase system. It is found that hydrophobic as well as charge interaction between a substance partitioned in the system and the micelles are predominant factors that govern the extraction. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Cationic and anionic surfactants; Aqueous two-phase; Extraction; Dyes; Porphyrin and metalloporphyrin compounds 1. Introduction Surfactants have been employed with great success in photometric [1], ¯uorometric [2] and phosphori- metric [3] determinations for their favorable proper- ties to enhance the solubility and detection sensitivity of analytes. Surfactants also play an important role in separation science. For example, aqueous micellar solutions are used as the mobile phase in micellar liquid chromatography [4] as well as used in the electrolytic mobile phase of micellar electrokinetic capillary chromatography [5]. A well-known phase separation method, namely, the cloud-point extrac- tion, utilizes the cloud-point feature of non-ionic or zwitterionic surfactant. Such a temperature induced phase separation [6,7] has been successfully used in the extractive preconcentration, separation and/or pur- i®cation of various species, ranging from metal che- lates, organic compounds of environmental concern, Analytica Chimica Acta 369 (1998) 11±16 *Corresponding author. Fax: +86 1062 770327. 0003-2670/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. PII S0003-2670(98)00209-8