Bio-Rad PROTEAN® Plus Hinged Spacer Plates and Combs - Manual (Page 9)

Section 6
Gradient Former Care and Maintenance
After use, disassemble the gradient former and rinse all parts with distilled water. If the
gel polymerizes in the gradient former during casting or before the system can be flushed
with water, the unit can be easily cleaned. The valve stem and stopcock are easily removed.
The needle will probably have to be replaced (catalog number 165-2007). The polymerized
gel can usually be removed from the tubing, the Luer coupling, and Y-connector with a little
effort, or you can replace them with the Tubing Connection Kit (catalog number 165-2008).
Use no organic solvents, strong acid solutions, or ethanol in the gradient former.
Section 7
Theory of Linear and Exponential Gradient Gels
7.1 Linear Gradients
Linear gradients are described by the equation:
Ct = CM + (CR - CM) Vt/2Vo
where Ct = concentration of gradient being delivered at any time,
CM = initial concentration in mixing chamber,
CR = concentration in reservoir,
Vt = volume delivered at time t,
Vo = original volume in each chamber.
A typical linear gradient is shown in Figure 7.1. The slope of the gradient is changed by
changing the acrylamide concentration in the mixing and/or reservoir chamber.
7.2 Exponential Gradients
Both convex and concave exponential gradients are described by the equation
Ct = CR - (CR - CM) e - Vt/VM
where e = natural base (2.718), and
VM = volume of acrylamide in the mixing chamber; the other symbols are as above.
Figure 7.2 and 7.3 show how a concave gradient is set up in the gradient former, how the
gel pore size varies with the length of the gel, and how the % acrylamide varies with the
amount of acrylamide delivered.
Figure 7.4 and 7.5 show how a convex gradient is set up in the gradient former, how the
gel pore size varies with the length of the gel, and how the % acrylamide varies with the
amount of acrylamide delivered.
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