| Abstract
| - Recent advances in the analysis of nanoliter volumes using1H NMR microcoils have led to the application of microcoils as detectors for capillary electrophoresis (CE).Custom NMR probes consisting of 1-mm-long solenoidalmicrocoils are fabricated from 50-μm diameter wirewrapped around capillaries to create nanoliter-volumedetection cells. For geometries in which the capillary andstatic magnetic field are not parallel, the electrophoreticcurrent induces a magnetic field gradient which degradesthe spectroscopic information obtainable from CE/NMR.To reduce this effect and allow longer analyte observationtimes, the electrophoretic voltage is periodically interrupted so that 1-min high-resolution NMR spectra areobtained for every 15 s of applied voltage. The limits ofdetection (LODs; based on S/N = 3) for CE/NMR forarginine are 57 ng (330 pmol; 31 mM) and for triethylamine (TEA) are 9 ng (88 pmol; 11 mM). Field-amplifiedstacking is used for sample preconcentration. As oneexample, a 290-nL injection of a mixture of arginine andTEA both at 50 mM (15 nmol of each injected) is stackedseveralfold for improved concentration LODs while achieving a separation efficiency greater than 50 000. Dissolvinga sample in a mixture of 10% H2O/90% D2O allows H2Oto serve as the nearly ideal neutral tracer and allows directobservation of the parabolic and flat flow profiles associated with gravimetric and electrokinetic injection, respectively. The unique capabilities of CE and the rich spectralinformation provided by NMR spectroscopy combine toyield a valuable analytical tool, especially in the study ofmass-limited samples.
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