Nuclear magnetic resonance (NMR) spectroscopy is performed by exposing a material sample to a magnetic field. Material samples are generally liquid but can also be gaseous or solid. The sample is placed within a sample tube that is placed in the magnetic field. The nuclear spins of the atoms within the material sample come into an equilibrium in the presence of the magnetic field which aligns the nuclear spins of atoms within the material sample. After alignment, the material sample is exposed to electromagnetic energy having a radio frequency that perturbs the nuclear spins of the atoms from their equilibrium. As the perturbed nuclear spins return to equilibrium, energy in the form of a second electromagnetic radio frequency unique to the environment of the atoms is observed and measured.
NMR is used for research to study chemical behavior of many compounds. Because compounds behave differently at different conditions of temperature and pressure, it is necessary to perform NMR spectroscopy at different conditions to obtain a thorough understanding of the chemical behavior of a particular compound over a wide range of conditions.
However, performing tests at high pressures, particularly as high as 4 kbar and above, using NMR is difficult. The vessel containing the material sample must be non-magnetic and must have sufficient mechanical strength to withstand the stress induced by the internal pressure.
This problem has been recognized and various approaches taken. In an article NUCLEAR MAGNETIC RESONANCE AND LASER SCATTERING TECHNIQUES AT HIGH PRESSURE, Jiri Jonas, High Pressure Chemistry and Biochemistry, pp. 193-235, 1987, several devices for achieving high pressure NMR spectroscopy are disclosed. Pressures ranging from 0.062 kbar to 9 kbar are achieved with the devices shown in FIGS. 4, 5, and 6 of Jonas. These devices have two common characteristics. First, they are straight, once-through vessels, and second, they are custom designed for a particular spectrographic measurement and are neither interchangeable nor broadly useful for a variety of measurements.
Another article, PRESSURE-RESISTING GLASS CELL FOR HIGH-PRESSURE, HIGH-RESOLUTION NMR MEASUREMENT, Hiroaki Yamada, Rev. Sci. Instrum., Vol. 45, No. 5, May 1974, discloses achievement of test pressures up to about 2 kbar with a glass capillary vessel. Further disclosed are the details of construction of the once-through capillary and connection to a standard high pressure tube.
A third article, SOME ASPECTS OF HIGH-PRESSURE NMR, I Ando and G. A. Webb, Magnetic Resonance in Chemistry, Vol 24, pp. 557-567 (1986) discusses the use of non-magnetic materials for NMR vessels, in particular, metals including stainless steel, beryllium copper alloy and titanium alloy, and glass in the form of glass capillary.
A fourth article, GLASS CAPILLARY FOR HIGH RESOLUTION NMR MEASUREMENTS AT PRESSURES UP TO 400 MPa, R. K. Williams, Rev. Sci. Instrum. 49(5), May 1978, discloses use of Pyrex glass tubing cleaned in hydrogen fluoride then drawn to form a capillary vessel.
While there are many embodiments of NMR sample vessels having high pressure capability, each one is uniquely designed for spectroscopy of a particular material or to obtain a particular spectroscopic result and are not interchangeable. All of the designs have limited sample volume, thereby limiting the spectroscopic measurements that may be performed. Some designs prohibit the technique of spinning the sample to obtain greater line-width resolution.
Sample vessels made of glass or other brittle materials, for example sapphire, fail catastrophically, thereby potentially damaging equipment and/or injuring personnel. Copper-beryllium alloy is expensive and difficult to machine because of toxicity and hardness of the alloy.
It is therefore desirable to those skilled in the art of NMR measurements to have an NMR sample vessel capable of withstanding high pressure and having the capability of providing a variety of NMR spectrographic measurements. It is further desirable to have such a vessel for other types of spectrometry, for example electron spin resonance spectroscopy (ESR), where measurements at high pressure are desired.