Berkeley unveils portable high-res NMR sensor
high-resolution NMR spectroscopy, one of the principal tools for
chemical analysis, out of the laboratory and into the field for use
on samples of any size.
The device has the added advantage of not competing with superconducting magnets that are used to study proteins. The device also has applications in homeland security where samples from the field cannot be bought into the laboratory.
The device will therefore have applications in the medical diagnosis field and archaeological analysis. The developers also envisage this device as having use in the exploration of objects in space, like planets or moons.
This portable NMR sensor was developed by a collaboration of researchers with the US Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), the University of California at Berkeley and the Institute for Technical Chemistry and Macromolecular Chemistry in Aachen, Germany.
NMR is a phenomenon involving the atomic nuclei of molecules in which at least one proton or neutron are unpaired. The imbalance causes such nuclei to spin on an axis like miniature tops and gives rise to a magnetic moment, which means the nuclei act as if they were bar magnets with a north and south pole.
When a sample is exposed to a strong external magnetic field, these spinning "bar magnets" attempt to align their axes along the lines of magnetic force. The alignment is not exact, resulting in a wobbly rotation about the force lines that is unique for each type of nuclei.
If, while exposed to the magnetic field, the nuclei in a sample are also hit with a radiofrequency (rf) pulse, they will absorb and re-emit energy at specific frequencies according to their individual rates of rotation. These frequencies show up in an NMR spectrum as distinct peaks of varying height that, like a set of fingerprints, can be used to identify the sample's constituent nuclei.
Because the rate at which resonating nuclei realign themselves with magnetic field lines is heavily influenced by their neighbouring nuclei, NMR can also be used to provide detailed information on the structural, dynamic, and spatial relationships of atoms in a sample.
Deviations from reference peaks on the NMR spectrum, called "chemical shifts," reflect different concentrations of a sample's constituent nuclei and can be used to positively identify the molecular composition and chemical nature of the sample.
Until recently, high resolution NMR spectroscopy could only be done by placing a sample inside the bore of a very large stationary magnet that produces a strong, uniform magnetic field. Portable NMR systems with open, single-sided probes have been built, but the lack of uniformity in their magnetic fields limit them to low resolution.
"The variations within the magnetic fields of previous portable NMR devices are usually orders of magnitude too large to detect chemical shifts," said chemical engineering graduate student Vasiliki Demas, one of the co-authors of a paper describing the portable NMR device.
"These devices mainly yield relaxation times as a crude estimate of a sample's composition," he added.
The article appears in the April 8, 2005 issue of the journal >Science.
