Following the lead of astronomers who build their telescopes on remote mountaintops, German researchers have taken to the woods to generate ultrahigh-precision chemical measurements. By fleeing the magnetic interference common to civilization, a team at Forschungszentrum Jülich and Aachen University has devised a low-tech version of nuclear magnetic resonance (NMR) spectroscopy that can outperform multimillion-dollar lab instruments. The tabletop-sized device could hold the key to a new low-cost version of NMR spectroscopy.
NMR works because some atomic nuclei behave like tiny bar magnets. In typical NMR experiments, researchers place a chemical sample at the center of a giant high-field superconducting magnet that causes the nuclear spins to wobble--or "precess"--around the magnetic field at a rate that is unique for each atomic species. Next, they hit their sample with radio pulses that nudge the nuclear spins away from their normal orbit; the timing of their realignment betrays their identity and chemical neighbors. The larger the external magnetic field, the easier it is to see the signal, which makes it possible to work out the structure of larger and more complex molecules.
The new technique makes use of another NMR signal, called the "J-coupling," which doesn't depend on the external field. When J-coupling occurs, the spins of atomic nuclei affect the behavior of the electrons that form the chemical bonds between the atoms. This influence shows up on an NMR spectrometer as patterns that reveal the structure of the component molecule.
Tracking J-coupling in a lab is a challenge, because even a nearby screwdriver can create imbalances in the magnetic field that wash out its signature. Ultrasensitive superconducting detectors called SQUIDs can overcome the problem, but they are costly and need expensive cooling equipment.
So the German team--Stephan Appelt, Holger Kühn, and F. Wolfgang Häsing at the Forschungszentrum Jülich, and Bernhard Blümich at Aachen University--opted to do away with extra equipment by working in a forest 30 kilometers from Jülich. By escaping the magnetic interference of civilization and placing magnetic shielding around their electronic gear, the scientists obtained J-coupling information at least 10 times as precise as with superconducting magnets 100,000 times more powerful, they report online 22 January in Nature Physics.
"It's a very beautiful piece of work," says Alexander Pines, a chemist at the University of California, Berkeley, and a pioneer in low-field NMR. He predicts that because the technology is cheap and mobile, it could lead to easier ways to monitor chemicals during manufacturing and track chemical spills.
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