Separation Power of Steady-State Methods

In isoelectric focusing, as in electrophoresis, the force acting on a species having z elementary charges is zSFE, Eq. 8.8. Charge z, of course, is zero at the isoelectric point, equivalent to the focusing point, y = 0. At positions close to y = 0, z increases as follows 

Velocity U is simply the force divided by friction coefficient / 

It was shown in Section 6.1 that a component focused at y = 0 by the velocity expression W-U --ay would form a Gaussian zone centered at y- 0. Equation 6.18 shows that the r of the zone is (Dr/a)1/2. In the absence of convection, Drcan be replaced by molecular diffusion coefficient D, yielding 

Although the component zones are Gaussian, plate height expressions are meaningless because the zones (and the resulting separation structure) do not evolve continuously as a result of steady migration. However, resolution and peak capacity are still valid indices of separation, as discussed below. 

To calculate resolution, we need the distance LX between the centers of the two zones of interest as well as mean zone width 4o. The distance LX can be written as [50] 

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