Retention retardation factor

Recovery factor Reduced column length Reduced plate height Reduced velocity Relative retention ratio Retardation factor d Retention time Retention volume Selectivity coefficient Separation factor... 

Radioactive label, 330 Raman diffusion, 184 Raman scattering, 227 Ratio fluorimeter, 228 Rayleigh scattering, 226 Real mean, 385 Red-shift, 196 Reference electrode, 347 Reflectron, 298 Refractive index detector, 59 Relative response factor, 78 Relative standard deviation, 387 Reliability, 389 Resolving power, 282 Response factor, 77 Restrictor, 98 Retardation factor, 88 Retention factor, 14 Retention index, 41 Retention time, 7 Retention volume, 14 RP-18, 53 RSD, 387 Ruhemann, 112... 

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... 

Figure 5.7. Comparison of equations for calculating retention ratio Rr and retardation factor Rf. Reprinted courtesy of Gow-Mac Instrument Co.

Also, there are some operational differences that cause differences between the retention ratio and the retardation factor. Even if the exact same stationary phase is coated on a TLC plate and packed in a column, the TLC material usually contains an additional binder to hold the stationary phase on the plate. This binder will most likely alter slightly the characteristics of the stationary phase and result in differences between... 

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. 

In gas chromatography the analyte partitioning between mobile gas phase and stationary liquid phase is a real retention mechanism also, phase parameters, such as volume, thickness, internal diameter, and so on, are well known and easily determined. In liquid chromatography, however, the correct definition of the mobile-phase volume has been a subject of continuous debate in the last 30 years [13-16]. The assumption that the retardation factor, i /, which is a quantitative ratio, could be considered as the fraction of time that components spend in the mobile phase is not obvious either. 

The lipophilicity indices measured by RP-TLC and HPLC are derived from the retardation factor Rf and the retention time h, respectively. R( and h are converted to the logarithm of the capacity factor ( M/log Id) via Eqs. 1 and 2 ... 

Similar to the retention factor in HPLC the retardation factor Rf describes retention behavior during TLC experiments. It represents the ratio of the distance migrated by the sample to the distance traveled by the solvent front. Boundaries are 0 < R < 1. For Rf = 0, the product does not migrate from the origin and for R = 1, the product is not retained. Rf values are calculated to two decimal places, while some authors prefer to tabulate values as whole numbers, as hR values (equivalent to 100Rf) (Poole, 2003). 

In gas chromatography (GC) the mobile phase is a gas (e.g. nitrogen, N ) and moves rapidly compared to the movement of the separated substances. Thus, R values (retardation factor, i.e. the distance travelled by an analyte divided by the distance travelled by the mobile phase (these values are routinely used in TLC)) would be very small and hard to determine. Retention times are therefore employed in preference to Revalues. The retention tune of a compound (also used in liquid chromatography) may be described simply as the length of time it takes a compound to be detected following injection. This quantity has units of time, that is, seconds or minutes. 

Large retardation factors can mean that the leaching of metal cations from the soil surface into the subsoil is slow, even assuming that metal adsorption is by exchange processes only. As will be explained in Chapter 4, many metals adsorb in addition by strong forces, and this form of metal retention in soils is likely to be practically irreversible, leading to long-term immobilization. 

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. 

Rf value retardation factor in TLC and PC as a measure of the retention of a component on the stationary phase as it is carried along in the mobile phase ... 

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... 

The retention factor k can also be expressed in terras of the retardation factor by rewriting Equation 28-15 in the form... 

Because both of these volumes can be obtained from a chromatogram, the retardation factor is easily evaluated, as was the case for the retention factor. 

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