Batch equilibrium method coefficient

Under this umbrella, a number of different applications lie, amongst others the batch equilibration and equilibrium soil solution methods. According to the USEPA (1999), the former represents the most common laboratory method for determining partition coefficients—normally defined as Kd—both for contaminated sites studies and for predictions of chemicals behaviour in soils (OECD, 2002). The batch equilibration method consists of mixing a soil with a known amount of liquid (background electrolyte), which is then shaken into a slurry and allowed to equilibrate for an adequate time. The solution will be separated from the solids by centrifuging the slurry, resulting in a supernatant and a separated solid phase. The supernatant will, therefore, be removed, filtered and analysed. 

Celorie, J. A., Woods, S. L., Vinson, T. S., and Istok, J. D. (1989). A comparison of sorption equilibrium distribution coefficients using batch and centrifugation methods. J. Environ. Qual. 18... 

Adsorption of Strontium in Equilibrium-Type and Column Experiments. Laboratory batch equilibrium experiments were used as a rapid method for selecting ion exchangers for testing in columns. Distribution coefficients were obtained for strontium adsorption by equilibrating 1 g of resin or zeolite in 100 ml of basin water and agitating for 24 hr at ambient temperature. After centrifuging, the concenti ation of strontium-90 in the supernate was determined. Table VI shows the measured dis-... 

Since the adsorption coefficient is critical to the theoretical development, caution should be exercised in using a particular K value for a particular soil and pesticide. The most common method used to measure adsorption is by the batch equilibrium technique, in which soil samples are equilibrated with a series of pesticide concentrations. However, the equilibrium time is critical, and may not represent adsorption under field conditions where the pesticide is moving in the solution phase. Consequently, flow equilibrium methods have also been developed (29). 

Table 3.3 shows the effect of method on ka values. The type of method clearly affected the ka values and, although not shown, the time required for equilibrium in potassium adsorption to be reached. In earlier work, Ogwada and Sparks (1986a) had found that with the vortex batch method, diffusion was reduced significantly and the rate coefficients one obtained approximated reaction-controlled rate constants. The data in Table 3.3 show clearly that significant diffusion exists with the static and miscible displacement methods because of limited mixing. 

The template 7a can be split off by water or methanol to an extent of up to 95% (Scheme 2-5). The accuracy of the steric arrangement of the binding sites in the cavity can be tested by the ability of the polymer to resolve the racemate of the template, namely of phenyl-a-D,L-mannopyranoside. Therefore the polymer is equilibrated in a batch procedure with a solution of the racemate under conditions under which rebinding in equilibrium is possible. The enrichment of the antipodes on the polymer and in solution is determined by measuring the specific optical rotation and the separation factor a, i.e., the ratio of the distribution coefficients of the D and L compounds between polymer and solution, is calculated. After extensive optimization of the procedure, a values between 3.5 and 6.0 were obtained [10]. This is an extremely high selectivity for racemic resolution that cannot be reached by most other methods. 

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