Isotachophoresis is a method of electrophoresis that employs the basic principles of the stacking gel phase of multiphasic systems discussed in the preceding section. Employing nonsieving media, often low percentage polyacrylamide, isotachophoresis in its simplest form can be thought of as a stacking gel alone, without the separation gel. The principles are the same. With applied electric field, like-charged ions begin to separate by electrophoretic mobility. As the faster component begins to move away, a region of unbalanced counter-ions forms behind it. Associated with this region of unbalanced counter ions is a zone of higher voltage, a Kohlrausch discontinuity, which pulls the next fastest component along at the same speed. Although technically, isotachophoresis separates samples by electrophoretic mobility, the layers of sample molecules move at the same speed.

While generally not achieving the resolution of other forms of electrophoresis, isotachophoresis has been successfully employed for difficult samples, such as very small peptides, not amenable to traditional techniques. Isotachophoresis has also shown great promise for the analysis of complex mixtures of molecules of different classes.

NEXT TOPIC: Buffer Additives