Selective adsorption and partitioning of nonionic surfactants onto solids via liquid chromatograph mass spectra analysis

The sorption characteristics of three Triton series surfactants (Triton-100, Triton-305, and Triton-405) from aqueous solution onto four different solids with a wide range of organic matter (OM) content were studied through the liquid chromatograph mass spectrometry (LC-MS) analysis. The examined surfactant concentrations ranged from below to above the critical micelle concentration (CMC) of the selected surfactants. A parameter, Φ, defined as the ratio of the average ethylene oxide (EO) number of surfactant on the adsorbed phase to that in the aqueous solution, was used to distinguish the controlling mechanism (adsorption or partitioning) of surfactants from aqueous solution onto the solids. For solids with very low OM content, adsorption was the primary mechanism and the Φ values were found to be larger than 1.0 and might reduce to 1.0 with the increasing surfactant concentration. On the other hand, the Φ values for solids with very high content of OM were equal to or less than 1.0 and remained constant as the surfactant concentrations varied, in which partitioning was the most likely dominant mechanism. For solids with an intermediate content of OM, adsorption and partitioning mechanisms coexisted and the Φ values could be larger or less than 1.0 and decreased with the increasing surfactant concentration.