NMR Flow Probe for Fast Moving Fluids

Technology

The NMR flow probe comprises a probe body with an inlet and outlet, a first transmit coil, a second receive coil, and a switch circuit. First, the long transmit coil is used to excite nuclear magnetization over a large volume of sample such that fluid movement does not affect the signal during long relaxation or NMR experiments. The maximum flow rate is bound so that only sample that has spent the entire duration of the experiment within the transmit coil flows through the receive coil. The smaller receive coil detects radio frequency radiation only from this fluid, making the received signal independent of flow velocity. This configuration enables MR relaxometry and spectrometry to be applied to processes with high or variable flow rates without requiring knowledge of the instantaneous flow rate at every point in time during the experiment.

Problem Addressed

NMR spectroscopy and relaxometry can provide valuable monitoring of chemical reactions, bioprocess development, and the manufacturing of pharmaceuticals and foods. However, conventional NMR measurements are largely limited to static samples because these measurements often require observation of excited nuclear magnetization over several seconds, during which rapidly moving fluids may carry the excited portion of the sample out of the measurement coil. Several workarounds have been proposed for performing NMR measurements on moving samples. These approaches—such as retrospective mathematical correction, reduced flow rates, or the use of low‑pulsation pumps to maintain consistent flow—can increase system complexity, introduce additional limitations, and reduce flexibility. The present disclosure addresses these challenges by providing coil geometries for a flow probe that enables NMR experiments on rapidly moving fluids, such as those encountered in bioprocess monitoring.

Advantages

• Well suited for continuous bioprocess monitoring with magnetic relaxometry at high flow rates and during long Carr‑Purcell‑Meiboom‑Gill experiments
• Enables long relaxation measurements on fast‑moving or pulsating fluids, including peristaltic flow
• Eliminates the need for measurement of instantaneous flow rates or retrospective mathematical corrections
• Enables cell density measurements on perfusion bioreactors without an additional pump or branch in the system
• Reduced system complexity compared to low‑pulsation pumping or stop‑flow approaches
• Can enable flow‑rate agnostic Liquid Chromatography–Nuclear Magnetic Resonance measurements, avoiding diffusion‑induced peak broadening from flow slowing
• Allows NMR experiments designed for stationary samples to be applied directly to moving samples