Migration distance

The fundamental parimeter used to characterize the position of a saaple zone in a TLC chromatograa is the retardation factor, or Rf value. It represents the ratio of the distance migrated by the saaple compared to that traveled by the solvent front. With respect to Figure 7.1, the Rf value for linear development is given by equation (7.1)... 

Therefore, the sequence of reactions illustrated in Fig. 1 catalytically (the anthraquinone is regenerated) injects a radical cation into a DNA oligonucleotide that does not simultaneously contain a radical anion. As a result, the lifetime of this radical cation is determined by its relatively slow bimolecular reaction with H20 (or some other diffusible reagent such as 02- ) and not by a rapid intramolecular charge annihilation reaction. This provides sufficient time for the long distance migration of the radical cation in DNA to occur. 

Fleischer, R. L. and A. Mogro-Campero, Mapping of Integrated Radon Emanation for Detection of Long-Distance Migration of Gases Within the Earth Techniques and Principles,. 1. Geophvs. Res. 83(B7) 3539-3549 (1977). 

Ionic strength t in Distance migrated Electrophoretic mobility... 

Figure 7.1 Separation of proteins by SDS-PAGE. Protein samples are incubated with SDS (as well as reducing agents, which disrupt disulfide linkages). The electric field is applied across the gel after the protein samples to be analysed are loaded into the gel wells. The rate of protein migration towards the anode is dependent upon protein size. After electrophoresis is complete, individual protein bands may be visualized by staining with a protein-binding dye (a). If one well is loaded with a mixture of proteins, each of known molecular mass, a standard curve relating distance migrated to molecular mass can be constructed (b). This allows estimation of the molecular mass of the purified protein...

During the migration of cations and anions towards their respective electrodes, each ion tends to carry solvated water along with it. As cations are usually more solvated than anions, a net flow of water towards the cathode occurs during the separation process. This effect, known as electro-osmosis, results in a movement of neutral species which would normally be expected to remain at the point of application of the sample. If required, a correction can be applied to the distances migrated by ionic species by measuring them... 

It is seen from the contents of heavy metals in stream sediments, soils and suspended matters for the main basins of the Anhui section of the Yangtze River that the contents of heavy metals in suspended matters are obviously higher than those in stream sediments and soils, indicating that the suspended matters are the main carriers for long distance migrations of heavy metals in the Yangtze River basin. 

For the determination of DNA size suitable markers are included in one of the lanes. A straight line calibration graph can be obtained by plotting distance migrated against log10 base pairs of the markers. 

Pore-gradient SDS-PAGE gels can also be used to estimate molecular masses. In this case, log Mr is proportional to log (%T). With linear gradients,%T is proportional to distance migrated, so that the data can be plotted as log Mr vs. log (migration distance). 

Therefore both types of dispersion will be proportionate to the square root of the distance migrated. If they add as a simple vector sum, (which may be a gross simplification) then ... 

In order to calculate the retention factor k of a compound or the selectivity coefficient between two compounds, the distance migrated along the plate is usually translated into the migration time for the chromatogram. Assuming that the ratio of the migration velocities u/u0 is the same on the plate as on the column (this is only an approximation), then Rf can be related to k ... 

Measure the total length of the slab gel and the distance migrated by each protein and the tracking dye from the top. In your notebook, draw a picture of the gel showing protein bands. A photograph may be taken as a permanent record. 

The logarithm of the molecular weight of an SDS-denatured polypeptide scales linearly with the polypeptide s Rvalue [Eq. (9.18)]. The R value is calculated as the ratio of the distance migrated by the molecule to that migrated by a low-molecular-weight marker dye-front. 

Fig. 2. SDS-PAGE. (a) Appearance of proteins after electrophoresis on an SDS polyacrylamide gel. Lane 1, proteins (markers) of known molecular mass lane 2, unpurified mixture of proteins lane 3, partially purified protein lane 4, protein purified to apparent homogeneity (b) determination of the molecular mass of an unknown protein by comparison of its electrophoretic mobility (distance migrated) with those of proteins (markers) of known molecular mass.

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