Sedimentation isopycnic

Steady-State Zones in Free Space (Isoelectric Focusing and Isopycnic Sedimentation)... 

Figure 6.1. Steady-state Gaussian zone formed in methods such as isoelectric focusing and isopycnic sedimentation by the opposing interplay of a focusing force and diffusion. Different components focus at different locations to give separation.

Examination of the groupings of Table 7.2 verifies most of the more or less traditional associations between separation methods chromatography with countercurrent distribution and distillation, electrophoresis with rate-zonal sedimentation, isoelectric focusing with isopycnic sedimentation, re-... 

Associated with the new cmin class of profiles, we would find steady-state methods such as isoelectric focusing, isopycnic sedimentation, and some related methods that have been proposed [14]. The unique ability of these methods to separate mixtures into many zones or bands is related to the fact that the minimum for each component is found at a different point in space. 

STEADY-STATE VARIANTS OF Sc METHODS ISOELECTRIC FOCUSING AND ISOPYCNIC SEDIMENTATION... 

We found earlier that transient (nonsteady-state) sedimentation required density gradients to stabilize against convection. Isopycnic sedimentation relies on density gradients not only for anticonvective purposes but also as the secondary gradient needed to establish steady-state conditions. The difference in the two cases is found in the magnitude of the density gradient and in the degree to which components are allowed to approach their steady-state condition. The equipment is similar the zonal rotor developed by Anderson is used for isopycnic as well as transient zonal separations [45]. 

An integrated treatment of isoelectric focusing and isopycnic sedimentation was presented in 1971 [50] the following is based on that treatment. 

The final expression, Eq. 8.53, shows how the resolution of two species varies with their average molecular weight Af, the difference Aps in their density, the field strength G, and the density gradient dp/dx. Like Eq. 8.46 for isoelectric focusing, Eq. 8.53 can be used to quantitatively describe the parameters necessary for resolution in isopycnic sedimentation [50]. 

Peak capacity nc, like resolution, can be calculated in a straightforward manner for both isoelectric focusing and isopycnic sedimentation. However, it is most interesting to cast ne in a form such that these steady-state methods can be related to the analogous transient methods, namely, zone electrophoresis and rate-zonal sedimentation. To do this we substitute a from Eq. 8.42 into the basic peak capacity expression nc = L/4o-, Eq. 5.59. Then using D = 9177/, we get... 

When transversely oriented focusing forces of the type used in isoelectric focusing or isopycnic sedimentation are used to confine different components to different thin bands or laminae in an FFF channel, we have a variant of FFF called hyperlayer FFF. Suppose component A is focused at y = 15.2 /xm and B at y = 127 /xm (0.005 in). You may assume that the thin bands form a 6-function distribution in coordinate y and that channel thickness w = 254 /xm. What is the R value for each of the two components ... 

D. Rickwood, A. Hell, and G. D. Birnie, FEBS Lett., 33 221 (1973). Isopycnic Sedimentation of Chromatin in Metrizamide. 

The separation of different species in a centrifiigal force field (the imposed primary force field) having a radial density gradient (secondary physical property based field) is identified as isopycnic sedimentation or density-gradient sedimentation (Giddings and Dahlgren, 1971). Each species... 

Calculate the maximum number of macromolecular species whose peaks may be clearly resolved in isopycnic sedimentation if the cell length is 1.5 cm. For the purpose of calculations, use the data provided in the example given in the text to calculate the resolution (Rj for the isotopicaUy labeled and unlabeled DNA molecules in a CsCl gradient the density gradient is 0.08 g/cm. You may use the values of Rj or a developed/used in the text calculations for an estimate of the peak width. How does this number change if the Rj value is 1.5 (Ans. iax = 18.25 niax — 13.)... 

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