Sorption of octa(oxyethylene) monododecyl ether onto silica gel studied byliquid chromatographic methods

The adsorption of octa(oxyethylene) monododecyl ether (C12E8) from water on to silica gel-a system of technical as well as environmental interest-is in vestigated at various temperatures using liquid chromatographic techniques. The isotherms obtained are of the two-step type. The first step at low ads orbed amounts has scarcely been observed in the past. Therefore, this study focuses on this area. The sorption isotherms and the influence of temperat ure on these isotherms indicate different adsorption mechanisms for the two isotherm steps. Whereas the first step seems to be related to hydrogen bon ds between hydrophilic surfactant groups and surface silanol groups, the se cond step can be well explained by the formation of hemimicelles on the sur face. For the determination of the sorption isotherms, a liquid chromatogra phic technique, an elution analysis, is introduced. The so-called "elution on a plateau" technique measures the derivative of an isotherm and therefor e can provide additional details about the course of the adsorption isother m. In comparison with the common batch technique for the determination of s orption isotherms, the chromatographic method has several advantages. Tempe rature control of the measurement system is simpler. Furthermore, the inves tigation of the transport behavior and of poorly detectable substances such as poly(oxyethylene) monoalkyl ethers is possible.