Sorption-desorption kinetics, effect

Effect of the Counteranion Type and Concentration on Peak Efficiency and Asymmetry. Theoretically, a column can generate a certain maximum number of theoretical plates at the optimum flow rate. This number should be independent of the type of the analyte and mobile phase. In reality, any secondary processes, energetic surface heterogeneity, or restrictions in sorption-desorption kinetics in the column will result in the specific decrease of the efficiency for a particular compound. 

Using sorption-desorption kinetics, the extent of non-Fickian behavior decreases as the thickness of the film increases. Presumably, as the ratio of the time scale for diffusion to the time scale for stress-induced relaxation I ID) becomes large, the time-dependent relaxation occurs so rapidly (relatively) that it has a small effect on the diffusion process. In other words, in the limit where molecular-scale responses to swelling stresses are rapid compared to the rate of diffusion, the process appears to be Fickian. This is the case for totally amorphous rubbery polymers that behave as high molecular weight liquids. 

Pigna M, Krishnamurti GSR, Violante A (2006) Kinetics of arsenate sorption-desorption from metal oxides Effect of residence time. Soil Sci Soc Am J 70 2017-2027... 

Temperature has a marked effect on the kinetics of reaction rates of solid phase sorption/desorption processes [113-116]. Arrhenius noted the following relationship between k and T (Eq. 52) ... 

Inadequate understanding of the kinetics of the sorption/desorption process detracts from our ability to completely understand the effects of sorption on hydrolytic rates, and more research is needed in this regard. 

Scow, K. M. (1993)- Effect of sorption-desorption and diffusion processes on the kinetics of biodegradation of organic chemicals in soil. In Sorption and Degradation of Pesticides and Organic Chemicals in Soil, ed. D. M. Linn, T. H. Carski, M. L. Brusseau F-H. Chang, pp. 73-114. Madison, WI Soil Science Society of America, American Society of Agronomy. 

Laboratory experiments, transport modeling, field data, and engineering cost analysis provide complementary information to be used in an assessment of the viability of an MNA approach for a site. Information from kinetic sorption/ desorption experiments, selective extraction experiments, reactive transport modeling, and historical case analyses of plumes at several UMTRA sites can be used to establish a framework for evaluation of MNA for uranium contamination (Brady et al, 1998, 2002 Bryan and Siegel, 1998 Jove-Colon et al, 2001). The results of a recent project conducted at the Hanford 100-N site provided information for evaluation of MNA for a °Sr plume that has reached the Columbia River (Kelley et al, 2002). The study included strontium sorption-desorption studies, strontium transport and hydrologic modeling of the near-river system, and evaluation of the comparative costs and predicted effectiveness of alternative remediation strategies. 

Wall effects, or the adherence of material to the bare silica capillary wall, has been a difficult problem since the early days of HPCE, particularly for large molecules such as proteins. Small molecules can have, at most, one point of attachment to the wall and the kinetics of ad-sorption/desorption are rapid. Large molecules can have multiple points of attachment resulting in slow kinetics. Several solutions have been proposed, including the use of (a) extreme-pH buffers, (b) high-concentration buffers, (c) amine modifiers, (d) dynamically coated capillaries, and (e) treated or functionalized capillaries. 

Dissolved arsenic concentrations can be limited either by the solubility of minerals containing arsenic as a constituent element (or in solid solution) or by sorption of arsenic onto various mineral phases. For both the precipitation-dissolution of arsenic-containing minerals and sorption-desorption of arsenic onto solid phases, equilibrium calculations can indicate the level of control over dissolved arsenic concentrations that can be exerted by these processes. However, neither of these types of reactions is necessarily at equilibrium in natural waters. The kinetics of these reactions can be very sensitive to a variety of environmental parameters and to the level of microbial activity. In particular, a pronounced effect of the prevailing redox conditions is expected because potentially important sorbents (e.g., Fe(III) oxyhydroxides) are unstable under reducing conditions and because of the differing solubilities of As(V) and As(III) solids. 

Several other aspects of organophosphorus insecticide sorption require further study. Although sorption-desorption hysteresis (20), aging and bound residue formation (30) have been noted, the molecular mechanisms responsible for these phenomena have not been elucidated. The kinetics of organophosphorus insecticide release from soil particles including the effects of biosurfactants (31) have not been extensively investigated, nor have the effects of formulation ingredients on sorption processes (32). 

The reaction rate Rj in these equations is a catch-all for the many types of reactions by which a component can be added to or removed from solution in a geochemical model. It is the sum of the effects of equilibrium reactions, such as dissolution and precipitation of buffer minerals and the sorption and desorption of species on mineral surfaces, as well as the kinetics of mineral dissolution and precipitation reactions, redox reactions, and microbial activity. 

Over the last decade, some research has indicated that (1) partition coefficients (i. e.,Kd) between solid and solution phase are not measured at true equilibrium [51,59-61], (2) the use of equilibrium rather than kinetic expressions for sorption in fate and effects models is questionable [22-24,60,61], and (3) sorption kinetics for some organic compounds are complex and poorly predictable [22 - 24,26]. This is mainly due to what has recently been discussed as slow sorp-tion/desorption of organic compounds to natural solid phase particles [107, 162-164,166-182]. The following is a summary of some important points supporting this hypothesis [1,66,67,170-183] ... 

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