Migration kinetics

This directly coupled HPLC-NMR method has been used to investigate the acyl migration kinetics of individual isomers of 2-, 3- and 4-fluoro-, and 2- and 3-trifluoromethylbenzoyl-D-glucopyranuronic acid separated from an equilibrium mixture of the (3-1-O-acyl isomer, the a- and [3-2-0-acyl isomers, the... 

Fag time The time that a substance needs under given conditions to cross a functional barrier package construction and to reach the food contact surface. The migration kinetics of a functional barrier system are in general characterised by an initial time lag phase. 

Our study of migration kinetics of the acetyl group (Table I) indicated several conditions under which the 0-to-N acyl shift was slowed. The 0-to-N shift was pH sensitive, proceeding faster as the pH was raised (first section of Table I) however, it was strongly promoted by water as well in KNm the requirement for water was absolute — in its absence the 0-to-N shift rate was negligible (second section). Hydroxylic solvents could partly substitute for water. 

In the recent years, the occurrence of anilines, chloroanilmes, and benzidines in environmental waters has started to be of concern due to their widespread use in various industrial processes. Detection of these compounds is generally carried out with LC-ECD working in the amperometric mode using a glassy-carbon electrode. Problems encountered are similar to those for phenolic compounds and, therefore, confirmation is always necessary by UV, DAD, or, preferably, MS detection [6]. These compounds are also CE amenable and this approach is really promising in the sense of sensitivity and selectivity because humic and fulvic material can be separated from the analytes due to their different migration kinetics. 

R. Noyori developed a procedure that avoids migration of the double bond during acetalization of a, 3-unsaturated ketones (enones)A Treatment of the enone with the silylated diol l,2-bis[(trimethylsilyl)oxy]ethane in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate (TMSOTf ) affords the acetal without double bond migration (kinetic control). The stability of the Me3Si-0-SiMe3 formed (instead of HjO) drives the reaction to completion. Modifications of Noyori s procedure in which preparation of the silylated diol is circumvented have been reported. ... 

Johnson CH, Wilson ID, Harding JR, et al. NMR spectroscopic studies on the in vitro acyl glucuronide migration kinetics of Ibuprofen ((+/-)-(R,S)-2-(4-isobutylphenyl) propanoic acid), its metabolites, and analogues. Anal Chem. 2007 79(22) 8720-8727. 

It should be emphasized that the forgoing analysis compares only the relative importance of mass transport to electric migration. Kinetics resistance, which is not scale-dependent, will typically be the overall dominant resistive mechanism on small scales, prevailing over both the mass transport and the ohmic resistances. 

The effect of the Langmuirian sorption mode per se on migration kinetics is explored further in Fig. 18. The total immobilization limit (F = 0) has been arbitrarily selected in preparing curve (a) of Fig. 18. Clearly, other values of F could be treated as well. The K = 0 limit (Henry s law sorption) gives rise to much more rapid desorption than for K > 0 since the mean diffusion coefficient corresponding to Eq. (27) is equal to Dd when K = 0. For all values of K > 0, D < Dd and desorption is retarded, however total evacuation of the sample is eventually predicted at times which, although non-infinite, are indeed extraordinarily long. 

The marker (NaCl) was released extremely slowly (Fig. 19). When polymeric emulsifiers were used at both interfaces the release rates were extremely low. The authors also prepared emulsions with blends of the new polymeric emulsifiers and hydrophobic low-molecular-weight emulsifiers such as sorbitan esters (Span 80). It was found that the low-molecular-weight emulsifiers increased the release rates. The migration kinetics were strongly dependent on emulsifier concentration. The release rates were enhanced also when other emulsifiers, such as EDT-PGPR, were used in the internal interface. It was concluded that, while the polymeric emulsifiers, even if aggregating in the oil phase, are restricted in their solubilizing capacity as hydrophilic compounds, the hydrophobic monomeric emulsifiers (such as Span 80) can easily form, in the oil layer, reverse mi-... 

As a last example of the migration kinetic and the power of the interface driven segregation, Schulze et al. showed by Forward recoil spectrometry that amino end-group polystyrene could go through more than 5(X) nm of non-functional PS to reach the interface with PMMA during a vacuum annealing at 174 °C (Fig. 5.10) [81]. 

R. E. Mistier, Grain Boundary Diffusion and Boundary Migration Kinetics in Aluminum Oxide, Sodium Chloride, and Silver, Sc.D. Thesis, Massachusetts Institute of Technology, Cambridge, MA, 1967. 

Regime 1 Evaporation (or dissolution)-controlled kinetics. In the case of thin samples (fibres, films, coatings) and high additive diffusivity, additive evaporation (step 1 in Fig. 12.7) is the slowest step and thus controls the global migration kinetics. Its concentration C (into the polymer) decreases proportionally with time (see Fig. 12.8(a)) ... 

ABSTRACT. The effect of the electrolyte concentration and solvent on the electrochemical oxidation of Cr(CO)6 at microelectrodes has been investigated. It is shown that reproducible data are obtained in media without the deliberate addition of electrolyte or in very resistive solvents such as toluene. The voltammetric realises are interpreted in the light of ohmic drop, migration, kinetics and double layer effects. 

A second, more complex model which can approximate energy migration kinetics involves the relaxation of the condition that there must be an even distribution of chromophores. Such a relaxation can involve, say, a random distribution of chromophores in three dimensions interspersed by a random distribution of traps. The GAF [34] and LAF [35] models are of this type and, in addition,... 

Crank-Nicholson method, 301 Crystallite migration kinetics of, 218 mechanism of, 202... 

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