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A temperature-jump relaxation technique is used to monitor reversible adsorption/desorption kinetics at the reversed-phase C1 -silica/solution interface. A Joule discharge is used to heat a packed bed of trimethylchlorosilane-derivatized silica gel on a microsecond time scale. Single-exponential relaxation kinetics are observed for adsorption of an ionic fluorescent probe, l-anilino-8naphthalenesulfonate, to a Cl-silica surface from methanol/ water solution. The relaxation rate increases with concentration of solute in solution, which shows that adsorption kinetics are detectable in the relaxation. The adsorption rate of the ionic probe is slower than diffusioncontrolled, exhibiting significant influence over the adsorption equilibrium constant The adsorption rate of .ZV-phenyi-1 -naphthylamine is indistinguishable from the diffusion limit, indicating a negligible barrier to adsorption for this neutral species.Separations in reversed-phase liquid chromatography result from complex thermodynamic and kinetic processes involving the transfer of solutes between the mobile and stationary phases.Knowledge of kinetics in this process is important for the design of effective column materials and for fundamental understanding of the chemistry of bonded phases and the retention behavior of analytes. The kinetics of chromatographic retention on bonded hydrocarbon stationary phases are not well-understood. Two approaches to gaining information about adsorption/desorption kinetics in chromatographic systems have been developed.Chromatographic techniques have been used to investigate these kinetics by measuring plate heights versus flow velocity and correcting for the estimated contributions from dispersion and diffusion.1 Despite questions raised about the assumptions underlying this method1 2 and errors associated with the fitting of peak shapes to determine kinetic parameters,3 two general conclusions can be made from band-broadening studies of adsorption/desorption kinetics: that slow rates of desorption dominate kinetic contributions to band broadening and that barriers to adsorption are much smaller and difficult to detect in the shape of eluted peaks.A more direct approach to measuring adsorption/desorption rates is the use of relaxation kinetic methods. In relaxation kinetics, the equilibrium of a reversible process is shifted by a rapid change of conditions, such as temperature, pressure, or

Most of our understanding of chromatographic processes has been inferred from retention measurements. These measurements do not generally provide information about the role of sorption and desorption kinetics on retention equilibria. In this work, we show that temperature-jump relaxation techniques can be used to monitor reversible kinetics at the liquid/solid

A feasible and relatively readily available analytical method was adapted for the assessment of alcohol ethoxylates (AE) and fatty alcohols (FA) in sediments. This study illustrates the simultaneous measurement of 38 of 114 possible alcohol ethoxylate ethoxymers (AE) and fatty alcohols (FA) found in commercially important AE products. We predicted toxicity for all identified fractions, as well as the total mixture toxicity, relative to three exposure scenarios via sewage treatment plants (STP) for these widely used chemicals in consumer products and hence generate a preliminary environmental risk screening for AE and FA in sediments. The method is based on derivatization of solvent or solid-phase extracts with 2-fluoro-N-methylpyridinium p-toluenesulfonate (Pyr+). The derivatized extracts were analyzed with liquid chromatography/mass spectrometry (LC/MS) operating in the positive ion electrospray mode. The extraction efficiency of AE and FA in three different sediments of varying composition was evaluated with spike-recovery studies, ranging from 64% to 80%. The detection limits for individual ethoxymers typically ranged from 1 to 5 ngg(-1)on a dry weight basis. The mean limit of detection (LOD) was 6 ngg(-1)and the median LOD was 3 ngg(-1). AE and FA in sediments were found to be stable for two weeks if preserved with 3% (v/v) formalin and stored at 4-6( composite function)C. Based on equilibrium partitioning, background concentrations of AE and FA were predicted to be below concentrations known to elicit chronically toxic effects. Total worst case mixture toxicities for all AE ethoxymers combined with FA were predicted to result in a risk quotient less than 0.6. Activated sludge treatment (STP) significantly reduced the release of total AE and FA by four-fold, suggesting that the total mixture risk quotient would be < 0.15 for sediment dependent organisms.

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