PROBLEMS OF QUANTITATIVE INJECTION IN CAPILLARY ZONE ELECTROPHORESIS

CZE effective injection volumes are modified by two effects discussed in this article: diffusion and inadvertent hydrodynamic flow. Diffusion causes net flow into or out of the capillary whenever there exists a concentration gradient at the capillary inlet, and it is most important for small molecules, for short injection zones, and for slow injection sequences. Inadvertent hydrodynamic flow, most likely caused by a difference in levels of the liquids in the two reservoirs, is most important for liquid level differences of a few millimeters or more, for short injection zones, and for capillaries of short length and large inside diameter. Computer simulations of the first few millimeters of capillary length show how concentration profiles can develop rapidly.