Computer-controlled pulsed magnetic field gradient NMR system for electrophoretic mobility measurements

A computer-controlled pulsed magnetic field gradient NMR (PFGNMR) system for making electrophoretic mobility and diffusion measurements is described. Emphasis is placed on the design and capabilities of the gradient and electrophoretic pulse generators. Various pulse sequences can be applied by the programmable gradient generator that can produce 0- to 10-A current pulses for 0 to 13 ms and continuous currents from 0 to 50 mA. The pulse areas are reproducible to within approximately 1 ppm. A pair of opposed Helmholtz coils in the probe create linear magnetic field gradients during the current pulses. Electric fields are applied across a U-tube electrophoretic cell by a 550-V constant current generator.