Kinetic characterization rate-time curves

The kinetics at longer times were quite different. As shown in Figure 6-10, the initial period of gelation was characterized by concave cure curves, after which they became convex and then almost linear. At 5°C, the convex region was not perceptible. This different behavior, and the effect of temperature on the rate of aging of the HM pectin gels, could be clearly illustrated when the SDRs were analyzed at different aging temperatures. 

Pharmacokinetic parameters, such as elimination half life (ti/2), the elimination rate constant (K), the apparent volume of distribution (V) and the systemic clearance (Cl) of most drugs are not expected to change when different doses are administered and/or when the drug is administered via different routes as a single or multiple doses. The kinetics of these drugs is described as linear, or dose-independent, pharmacokinetics and is characterized by the first-order process. The term linear simply means that plasma concentration at a given time at steady state and the area under the plasma concentration versus time curve (AUC) will both be directly proportional to the dose administered, as illustrated in Fig. 15.1. 

A procedure for characterizing the rates of the volume change of gels has not been uniformly adopted. Often, the kinetics are simply presented as empirical sorption/desorption curves without quantitative analysis. In other cases, only the time required for a sample of given dimensions to reach a certain percentage of equilibrium is cited. One means of reducing sorption/desorption curves to empirical parameters is to fit the first 60% of the sorption curve to the empirical expression [119,141]... 

The voltammetric response depends on the equilibrium constant K and the dimensionless chemical kinetic parameter e. Figure 2.30 illustrates variation of A f, with these two parameters. The dependence AWp vs. log( ), can be divided into three distinct regions. The first one corresponds to the very low observed kinetics of the chemical reaction, i.e., log( ) < —2, which is represented by the first plateau of curves in Fig. 2.30. Under such conditions, the voltammetric response is independent of K, since the loss of the electroactive material on the time scale of the experiment is insignificant. The second region, —2 < log( ) < 4, is represented by a parabolic dependence characterized by a pronounced minimum. The descending part of the parabola arises from the conversion of the electroactive material to the final inactive product, which is predominantly controlled by the rate of the forward chemical reaction. However, after reaching a minimum value, the peak current starts to increase by an increase of . In the ascending part of the parabola, the effect of... 

After having characterized the kinetic and equilibrium properties of the individual fractions of the ion exchanger, it should now be possible to describe quantitatively the kinetics of the Cs /H exchange in an arbitrary mixture of the resin fractions without further adjustment of parameters. The experiment consisted in this case of stirring simultaneously 0.2 g air dry ion exchanger in the form of each of the above size fractions (corresponding to Q, = 0.842 mequiv i = 1-5) in the solution, while the initial and boundary conditions were the same as for the individual fractions described above (initially only Cs ions in solution c,q, = 0.00662 M, V = 302 mL = 3.16). The experimentally observed decrease of Cs ions in solution as a function of time (again determined by an immersed conductivity probe) is shown in Fig. 2 (top). To calculate this rate curve, Eq. 

The first series of kinetic curves (Figure 7.24) is characterized by three sections the first is rapid and short (the characteristic time is t 10 s), the second is practically linear with an almost constant rate of the process (the characteristic time is T =< 6x10 s) and in the third section the polymerization rate gradually and slowly decreases (the characteristic time is lO s). 

The kinetic curve of the changes in the ozone concentration at the bubbling reactor outlet (Fig. 10) is characterized by three different regions AB - fast ozone consumption after the addition of pyrocatechol, BC -steady-state part, when the rate of the chemical reaction becomes equal to the rate of ozone supply, and CD - the ozone concentration begins to rise up due to the p Tocatechol consumption. The BC part of the curve allows calculation of the rate constant, and based on the area below the curve ABCD - evaluation of the stoichiometry of the reaction. The straight line designated [03] is the ozone concentration at the reactor inlet. Curve 2 presents the o-quinone formation in the course of the reaction time. Its profile suggests the intermediate formation of o-quinone. 

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