NMR detection with multiple solenoidal microcoils for continuous-flow capillary electrophoresis

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Separation Science

Background:

• Nuclear magnetic resonance (NMR) spectroscopy is a sensitive analytical technique.
• Capillary electrophoresis (CE) is a powerful separation method.
• Hyphenating CE with NMR (CE/NMR) offers enhanced analytical capabilities but faces challenges with NMR probe sensitivity and spectral quality due to electrophoretic current.

Purpose of the Study:

• To develop a novel multiple solenoidal coil NMR probe for CE/NMR hyphenation.
• To overcome the spectral degradation issue caused by electrophoretic current in solenoidal microcoils.
• To achieve high-resolution NMR detection during continuous-flow CE separations.

Main Methods:

• A unique multiple solenoidal coil NMR probe was designed and implemented.
• The electrophoretic flow from a single capillary was split into multiple outlets, each with an NMR detection coil.
• A stopped-flow technique was employed, alternating CE flow between outlets to allow high-resolution NMR acquisition.

Main Results:

• The multiple coil probe successfully avoided NMR spectral degradation induced by electrophoretic current.
• Automated adjustment of magnetic field homogeneity for the active coil improved probe performance.
• Analysis of a <3 nmole amine mixture yielded NMR spectra with 1-2 Hz line widths.

Conclusions:

• The developed multiple microcoil CE/NMR coupling provides a robust method for high-resolution online detection.
• This approach enables continuous CE separation with stopped-flow NMR detection, overcoming previous limitations.
• The technique demonstrates significant potential for sensitive analysis of complex mixtures.