Field programming to achieve uniform sensitivity for on-line detection in electrophoresis.

Under constant applied electric field, an analyte band traverses an on-line detection zone in an electrophoretic separation at a velocity inversely proportional to the detection time. Because analyte bands migrate with different velocities, the sensitivity of the detection system to different species can vary significantly. One approach for overcoming this problem is to change the applied electric field, E, as a function of the separation time, tau, so that the velocity of an analyte band when it passes through the detection zone is independent of the analyte's electrophoretic mobility. A possible solution is to make E(tau) grow exponentially, but this procedure causes band compression. The preferred solution is to make both E(tau) and the distance between the starting position of the sample and the detection zone increase linearly with separation time. This approach can be implemented with either slab-gel or capillary electrophoresis.