Optosensing of cationic surfactants based on host-guest chemistry

An optode membrane for cationic surfactants is presented. Plasticized poly(vinyl chloride) (PVC) membranes incorporating the hexaester of calix[6]arene and the neutral H⁺-selective chromo-ionophore (ETH5294) have proved to be excellent reversible sensing devices for cationic surfactants as exemplified by cetyltrimethylammonium bromide (CTMAB). Based on host-guest chemistry, the guest molecule CTMAB was extracted into the PVC membrane, forming a host-guest adduct with the host molecule calix[6]arene ionophore and causing a concomitant release of a proton from the protonated ETH5294 into the solution. Upon deprotonation, ETH5294 undergoes a color change which can be used as a means for the quantitation of CTMAB. Unlike small inorganic cations, such as K⁺ and Na⁺, the experimental results show that the membrane response depends to a great extent on the migration process of CTMAB from the bulk of the solution to the membrane interface. A modified theoretical equation describing the membrane response on the CTMAB concentrations has been derived and shown to be in conformity with the experimental results. Copyright (C) 1998 Elsevier Science B.V.