Study of the influence of water matrix components on admicellar sorbents

Hemimicelle-based and/or admicelle-based solid-phase extraction (SPE) has recently been proved to be a fruitful strategy for the extraction and concentration of a wide variety of organic pollutants. This research focus on the effect of river and wastewater matrix components on the adsorption of sodium dodecyl sulfate (SDS) onto alumina, which is the most-used sorbent in hemimicelle-based and/or admicelle-based SPE, and we discuss the analytical consequences of the modifications observed. The effect of electrolytes (0.1 M NaCl), precipitating agents (127 and 333 mg L(-1) CaCl2) and major organic components in wastewater (19.8 mg L(-1) carbohydrates, proteins and fats and 10 mg L(-1) linear alkylbenzene sulfonates (LAS) and rivers (8 mg L(-1) humic acid) on the SDS adsorption isotherm was investigated. Also, the global effect of matrix components was assessed using a river sample. Three types of sorbents were considered (hemimicelles, mixed hemimicelles/admicelles and admicelles). Electrolytes were found to compete with surfactant molecules for charge surface sites in the early part of the hemimicellar region; precipitating agents yield insoluble salts with the aqueous surfactant in equilibrium with admicelle-based sorbents; and organic matter did not have any influence at all. The matrix component concentrations investigated were above the usual range present in rivers and wastewater, which makes this study applicable to a wide number of environmental water samples. From the results obtained, simple rules were established to prevent and detect matrix-induced surfactant adsorption modifications, which permits us to know, a priori, the suitability of these sorbents for a specific application and allows the development of more straightforward and robust methods.