Optimization in Static Field Sc Systems

Because the transport of large molecules is inherently sluggish (due to a large friction coefficient/, Section 4.13), the speed at which macromolecules are separated by electrophoresis and sedimentation becomes an important consideration in optimization. Since N measures the efficiency of separation, the ratio Nl time measures the time-based rate of generation of efficiency [1]. We clearly wish to maximize the Nit ratio. 

Quantity X/t is simply migration velocity U. If U is replaced by -(Ilf) dficxtldx9 as suggested by Eq. 3.19, we find 

This expression can be used as a basis for maximizing separation speed. 

The above conclusions are relevant in comparing gel electrophoresis and electrophoresis in free solution. The polymer strands of the gel network are necessary to produce a selective sieving effect, but they increase /. This, by itself, has no adverse effect on efficiency N, but by reducing mobility (Eq. 8.19), it reduces separation speed as expressed by Eq. 8.36. This loss of speed can be offset by increasing the temperature, thus decreasing the local viscosity of the solution between the polymer strands and correspondingly decreasing /. 

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