Retardation factor resolution

Diffusion and mass transfer effects cause the dimensions of the separated spots to increase in all directions as elution proceeds, in much the same way as concentration profiles become Gaussian in column separations (p. 86). Multiple path, molecular diffusion and mass transfer effects all contribute to spreading along the direction of flow but only the first two cause lateral spreading. Consequently, the initially circular spots become progressively elliptical in the direction of flow. Efficiency and resolution are thus impaired. Elution must be halted before the solvent front reaches the opposite edge of the plate as the distance it has moved must be measured in order to calculate the retardation factors (Rf values) of separated components (p. 86). 

Reduced parameters, 66-69 Refractive index (RI) detector, 206-207 Regular solution, 49 Relative retention, 20-21, 22, 77 Repeatability, see Precision Reproducibility, see Precision Resolution, 17-19, 55 Response factors (detector), 104, 125 Response time, 94 Retardation factor, Rf, 71 Retention index of Kovats, 78 Retention ratio, 11, 12, 71 Retention time, 6, 9 Retention volume, 9, 75 adjusted, 10, 75 corrected, 62-63, 75 net, 63, 75 specific, 110 Reverse phase LC, 158 Rohrschneider/McReynolds constants, 137-140... 

Since both these transport processes depend on the frictional coefficient of the molecule in the same way, this is a very reasonable assumption, and explains why under conditions of severe retardation zones remain extremely sharp. By application of Pick s laws, Richards and Lecanidou determine the evolution of the zone half-width with time, and derive the important result, confirmed by experiment, that the zone-width, provided the ratio of diffusion coefficient to retardation factor is of the right order, depends to only a slight extent on the width of the starting zone applied at one end of the gel. For typical conditions there is no detectable loss in resolution for an initial zone width of up to 2 mm, and even for a 1 cm column of RNA solution applied to the gel there is only a 25% increase in band width. 

The degree of retention of a component is called the retardation factor (Rf) and corresponds to the distance migrated by an analyte over the distance migrated by the solvent (also called solvent front). The expression of the movement of a substance in comparison to another is the retention ratio R. and corresponds to the distance migrated by analyte A over the distance migrated by analyte B. The Rf -value is the most commonly used term and a reasonable value for good resolution is about 0.4 to 0.8. 

Retardation factor in TLC, PC Corrected retardation factor Retention index, Kovat s RI Resolution between adjacent peaks Signal output from detector Separation number Stationary phase Time... 

Radial coordinate Reaction rate Particle radius Retardation factor Regulation term Resolution Reynolds number Specific surface area Schmidt number Shenvood number Stanton number Time... 

Retardation factor in column chromatography fraction of a sample component in a mobile phase Gas constant Peak resolution Detector sensitivity Support-coated open tubular (column)... 

The CRR mode involves retarding the electron kinetic energies to a constant ratio of H /H where H is the energy passed by the analyzer. Thus, the energies are retarded by a constant factor. Spectra acquired in this mode ate less easy to quantify, but small peaks at low kinetic energies ate readily detected. This mode of operation results in spectra of constant relative resolution throughout. The relative resolution is improved in this mode by a factor of E. ... 

If the separation factor is unity, the peaks coincide, and no separation has occurred. If the separation factor is 1.3, the column selectively retards one component 30% more than the other. The larger the a value, the easier the HPLC separation is to achieve however, an a value of 1.1-1.4 is typically desired. As we show later in this chapter, because resolution is influenced by three factors, separations can be attained for a values smaller than 1.1. In some modes of modern HPLC, meaningful resolution can be achieved with a values as low as 1.05, which means that the column retards the second component only 5% more than it retards the first component. 

The objective of all chromatographic separation is resolution. This experiment illustrates resolution and the factors that affect it. As discussed in Chapters 1 and 3 resolution cannot occur if the components are not partially retained or slowed down (retarded) by the column. Therefore, before calculating resolution, it is important to use the results of the experiment to calculate the fundamental chromatographic parameters of retention, capacity factor, selectivity, and efficiency. 

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