Incoming concentration profile

An exception occurs at the peak maximum. Here the concentration profile is momentarily flat so that incoming solute does not change the existing concentration level. Thus equilibrium is established. Consequently the peak center will move at a rate governed by equilibrium, and the migration equations (such as Eq. 9.3) based on equilibrium concentrations are valid. 

The development of the concentration profile for a grid electrode may then be considered to occur in two steps. First, the concentration profile grows into the space between individual wire electrodes perpendicular or orthogonal to the incoming light beam. In this situation the absorbance detected experimentally is not proportional to the concentration of product generated due to the com-... 

The model must deal with the situation encountered when the electrodes are coated with a polymer and ionic leakage eventually causes failure. Ionic species and molecules diffuse to the electrodes as migration takes place under the effect of the electric field, the latter governed by the electrolytic process. Before steady state is attained, there is a transient period during which the incoming diffused species and the migration component establish concentration profiles and an equilibrium ionic concentration at the electrodes. 

The furfural concentration, depending on the acid concentration, also features a profile in vertical direction. The incoming raw material contains, of course, no furfural, but as it enters cold, furfural vapors created further down condense on it, and this imparts some furfural to the surface of the incoming particles, from where the furfural enters the interior of the particles by diffusion. Further downward, at higher acidities, where furfural is actually formed in the interior of the particles, and where the stripping effect of the steam removes the furfural from the surface of the particles, the diffusion of furfural is in opposite direction, from the interior of the particles to their surfaces. 

From Fig. 1 and the above equations, one can see that the reaction distribution will depend on the various transport and reaction phenomena. For limiting cases, if one of the reactants is limiting in terms of transport or concentration, then the reaction or transfer current-density profile will be exponential towards the place with the incoming limiting reactant. If both are equally limiting, one obtains a parabolic reaction profile. If the reaction itself is limiting, then one obtains a uniform reaction profile. 

UV-Vis may be used in the QA laboratory to either determine the concentration of a particular component in an incoming ingredient (quantitative analysis) or to obtain an overall spectrum (scan from 200-700 nm). An overall spectrum has value in providing a profile for future reference of either new batches of an incoming ingredient or a newly made finished flavor. These determinations are often made on dilutions that are used for sensory testing and require only 30 sec to obtain. 

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