Solvent exchange module for LC-NMR hyphenation using machine vision-controlled droplet evaporation

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Biochemistry

Background:

• Proton nuclear magnetic resonance (¹H NMR) spectroscopy is a powerful analytical technique.
• Eluent exchange is crucial for sample preparation in NMR, but traditional methods can be time-consuming and inefficient.
• Automated and miniaturized sample preparation techniques are needed to enhance NMR analysis.

Purpose of the Study:

• To develop and validate a novel method for eluent exchange using pendant droplet evaporation for ¹H NMR.
• To assess the efficiency, recovery, and repeatability of the developed system for various analytes.
• To evaluate the system's suitability for hyphenation with liquid chromatography.

Main Methods:

• Utilized pendant droplet evaporation to concentrate analytes from 500 nL droplets.
• Employed machine vision (MV) to monitor droplet size and control heating rates for stable evaporation.
• Investigated the system's performance with tomato extracts, analyzing both polar and nonpolar compounds.

Main Results:

• Achieved up to 90% solvent exchange with good recovery and repeatability for tomato extracts.
• Successfully handled both polar and nonpolar analytes in a single run.
• Recovered volatile and thermosensitive compounds without significant losses, though some losses occurred with ethanol and propionate due to azeotrope formation.

Conclusions:

• Pendant droplet evaporation offers a comprehensive, automated, and user-friendly approach for eluent exchange in ¹H NMR.
• The system demonstrates high efficiency and broad applicability for diverse analytes, suitable for on- and off-line hyphenation with liquid chromatography.
• Further optimization may be needed for analytes forming minimum boiling azeotropes.