A new high pressure sapphire nuclear magnetic resonance cell

A new version of a single-crystal sapphire high pressure nuclear magnetic resonance (NMR) cell is described that is capable of controlling the sample pressure independent of the temperature. A movable piston inside the cell adjusts and controls the sample pressure from ambient conditions to 200 atm within +/-0.3 atm. The linewidth at half-height for a C-13 spectrum of carbon dioxide at 15 degrees C and 57.8 atm is found to be 0.5 Hz. The carbon dioxide gas/liquid phase transition is clearly observed by measuring C-13 chemical shifts as the sample pressure approaches equilibrium. The time required for this NMR cell to reach equilibrium with its surroundings is relatively short, usually 15-30 min. The cell body has the same outer dimensions of a standard spinning turbine and fits into a standard 10 mm commercial probehead capable of controlling the sample temperature using the spectrometer's variable temperature unit. The flexibility of the device and the increased speed in making the measurement is demonstrated. Such control of important thermodynamic variables facilitates the NMR study of important biochemical and chemical reactions in gas, liquid, and supercritical fluid environments. (C) American Institute of Physics.