Available online at www.sciencedirect.com Journal of Hazardous Materials 152 (2008) 330–336 Selective adsorption and partitioning of nonionic surfactants onto solids via liquid chromatograph mass spectra analysis Huan-Ping Chao a,∗ , Yi-Tang Chang b , Jiunn-Fwu Lee c , Chung-Kung Lee d , I-Chun Chen c a Department of Bioenvironmental Engineering, Chung Yuan Christian University, Chung-Li 320, Taiwan b Department of Safety Health and Environmental Engineering, Tung Nan Institute of Technology, Shen-Keng, Taipei 222, Taiwan c Graduate Institute of Environmental Engineering, National Central University, Chung-Li 320, Taiwan d Green Environment R&D Center and Department of Environmental Engineering, Vanung University, Chung-Li 320, Taiwan Received 26 January 2007; received in revised form 2 July 2007; accepted 3 July 2007 Available online 6 July 2007 Abstract 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. © 2007 Elsevier B.V. All rights reserved. Keywords: Organic matter; Surfactants; Partitioning; Adsorption 1. Introduction Surfactants are commonly used for various industrial and household activities. They may contaminate the soil and ground- water and have a negative impact on human beings and the environment. Aside from the potential pollution problems, sur- factants are also considered for the remediation of contaminated soils [1–5]. Therefore, in order to evaluate the possible con- tamination or application, a better understanding of surfactant sorption by soils is of great importance. The capacity of the surfactant uptake by the solids is mainly determined by the type of surfactants and the composition of solid [6–9]. The adsorption of cationic surfactant onto solids is dominated by electrostatic forces [10,11] and the uptake capac- ity is determined via the cation exchange capacity and surface ∗ Corresponding author. Tel.: +886 3 2654914; fax: +886 3 2654949. E-mail address: hpchao@cycu.edu.tw (H.-P. Chao). area of the solids [12]. The adsorption uptake of nonionic surfac- tants by solids is more complicated than for cationic surfactants. The surfactant properties including ethylene oxide (EO) num- ber and critical micelle concentration (CMC) value as well as the solid’s surface area, mineral phase composition, and organic matter (OM) contents are key factors in the determination of the uptake capacity [13–17]. Generally, on the basis of adsorptive mass, surfactants with a higher EO number would have a rela- tively higher adsorption to a given solid [18] as well as solids with a higher surface area may possess higher uptake capac- ity for a given surfactant. However, most of the commercially available nonionic surfactants consist of a mixture of different components and the adsorptive competition resulting from the difference in the affinity of the individual component of surfac- tants to the solid leads to the possibility of an estimation error for the overall surfactant adsorption. Although a number of studies have described the adsorption characteristics of individual non- ionic surfactant components onto the low OM content solids [15,16], the information of surfactant adsorption by solids with 0304-3894/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2007.07.001