Improved accuracy and precision in electrophoretic NMR experiments. Current control and sample cell design

Electrophoretic NMR has the capacity to provide unique physico-chemical information but is limited by a variety of experimental artifacts, such as thermal convection and electrolytic products in the sample. Here we present some simple modifications to the experimental hardware and protocol that, in a significant number of cases, can much improve experimental accuracy and precision. We show that one can strongly reduce artifacts in a symmetric sample cell with an appropriate feeding of current and with a porous plug suitably inserted. This latter feature requires that the electric field pulses across the sensitive volume are implemented as current-controlled pulses applied to the sample. Measurements with current-controlled pulses have the additional advantage of not requiring calibration with samples of known electrophoretic mobility.