Optosensing of cationic surfactants based on host–guest chemistry Original Research Article

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.