A high-pressure NMR probe for aqueous geochemistry

Area of Science:

• Geochemistry
• Analytical Chemistry
• Physical Chemistry

Background:

• Solution-state Nuclear Magnetic Resonance (NMR) spectroscopy is crucial for understanding chemical processes.
• High-pressure studies are essential for geochemical and chemical research.
• Existing high-pressure NMR probes have limitations in pressure range and sample volume.

Purpose of the Study:

• To develop and present a novel non-magnetic piston-cylinder pressure cell for solution-state NMR spectroscopy.
• To extend the accessible pressure range for NMR measurements in geochemical applications.
• To investigate pressure-dependent chemical equilibria and reaction kinetics.

Main Methods:

• Design and construction of a non-magnetic piston-cylinder pressure cell for NMR.
• Calibration of the pressure cell up to 20 kbar using in-situ ruby fluorescence.
• Measurement of pressure dependencies of NMR-active nuclei using a microcoil with minimal sample volume (10 μL).
• Application to (11)B NMR spectroscopy of boric acid-catechol equilibria.

Main Results:

• The developed pressure cell successfully operates up to 20 kbar.
• NMR measurements can be performed with as little as 10 μL of sample.
• Analysis of boric acid-catechol equilibria revealed a significant pressure-driven exchange rate.
• A negative pressure-dependent activation volume was observed, indicating increased solvation and electrostriction.

Conclusions:

• The new pressure cell significantly expands the accessible pressure range for solution NMR spectroscopy.
• The inexpensive probe design is particularly valuable for advancing aqueous geochemistry.
• The findings demonstrate the utility of high-pressure NMR for studying chemical dynamics and solvation effects.