NMR spectroscopy is an information-dense analytical technique used to characterize materials by quantifying and determining molecular structure. Current NMR methodology is primarily limited to single-sample measurements under low-throughput conditions, which is a persistent challenge. As a result, there needs to be more alignment between applications that require screening large parameter spaces and the desire to use this information-rich technique.
This study describes a novel approach for fully automated high-throughput nuclear magnetic resonance spectroscopy with high mass sensitivity that combines microfluidic technologies with micro-NMR detectors. A scalable, NMR-compatible, low-power, and cost-effective microfluidic system with a micro-saddle NMR detector rolled around a glass capillary flanked by two integrated impedance sensors for sample position and velocity measurement is developed.
The system works by inserting target sample plugs separated by an immiscible fluid into a flexible microfluidic tube. This sample train is underflowing and fed through the capillary with the micro detector and sensors. The impedance sensors detect the interface between the aqueous and oil plugs, which is then used by a microcontroller to synchronize the NMR spectroscopy acquisition regardless of flow velocities or sample volume.
The system was successfully tested for automating flow-based measurement in a 500 MHz NMR system with operational flow sensors, enabling high-resolution spectroscopy and NMR sensitivity of 2.18 nmol s1/2. The flow sensors could distinguish between the most common solvents due to absolute differences in relative permittivity of 0.2. A fully automated NMR measurement of nine individual 120 L samples was completed in 3.6 minutes, or 15.3 seconds per sample.
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