Evaluation of Interaction between Metal Ions and Nonionic Surfactants Containing Polyoxyethylene Chain by Measurement of Streaming Potential

Interactions between a nonionic surfactant, polyoxyethylene nonylphenyl ether (PONPE), and metal ions were evaluated by streaming potential measurements. A steaming potential under 0.25 MPa pressurization was measured with non-modified, ODS-modified, and PONPE-coated ODS-modified fused-silica capillaries and the surface charge density was estimated. A surface charge density of a POPNE-coated capillary increased with the increase in HCl concentration in the sample solution and the value became almost constant over the concentration of 100 mM, of which the value was about twice that for an ODS-modified capillary. The protonated polyoxyethylene (POE) chains in an acidic solution interact electrostatically with various inorganic anions with the order being the same as for general an anion exchange chromatography. Chloride complex of Au(III) interacts with the surface both electrostatically and non-electrostatically, and an increase in the Au concentration resulted in a negatively charged surface whereas the sample solution contained 100 mM HCl providing a positively charged POE chains. In a neutral solution, maximum adsorption amount of K+ to POE chains was approximately three times larger than that of Na+, that is, it was confirmed that the POE chains have a greater affinity for K+ than N+.