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A sideways look by NMR 19 n a standard NMR instrument, the an- whose fields are weak compared with the F chemical shift of a series of fluorialyte is placed inside the bore of a sole- those of larger instruments. These pernated compounds and is currently worknoidal magnet, where the magnetic field is manent magnets also introduce signifiing on proton shift detection, a key step cant field inhomogeneity, which causes uniform. That’s fine for a few milliliters to a usable device. The resolution obvariations that can be orders of magniof sample in a millimeter-sized opening tained by the investigators is equivalent tude larger than the chemical shifts. of a powerful superconducting magnet. to an 8-ppm shift in 3 min of data acquiVasiliki Demas and Juan Perlo, gradu- sition; their initial experiments took sevBut NMR is a laboratory technique, unate students in the Berkeley and Aachen able to analyze the paint on a large caneral hours. vas in a museum or seek out exploBlümich emphasizes that their sives in airport luggage. However, system is not a working instruthat could be about to change. An ment but a basic research foundainternational research collaboration tion for one. “This is a big step 1.4 mm recently reported the first step totowards building a device,” he 0.9 mm ward an NMR device for field applisays. “We have shown that it is rf coil Sample tube cations (Science 2005, 308, 1279). possible to obtain data in a low The research team, led by Bernfield, using a permanent magnet, 12 mm hard Blümich of RWTH Aachen within meaningful times.” Further Shimming unit University (Germany) and Alexanimprovements should allow sciender Pines of the University of tists to observe chemical reactions 28 mm California, Berkeley, and the and even obtain detailed informaLawrence Berkeley National Labtion about material structure. Magnet yoke 26 mm Main magnet oratory, has constructed an NMR Experts in the field agree on sensor with a single-sided open the potential of the research to probe. “We have used one-sided advance portable NMR. “This deA rectangular three-turn rf coil was used to both excite sensors for several years for matevelopment is very interesting and and detect sample nuclear spins. (Adapted with permisrials testing,” says Blümich, “but potentially important, depending sion. Copyright 2005 American Association for the Adonly to measure relaxation times. on the degree to which it can be vancement of Science.) This development is the first step extended to a working portable toward a device that can measure the labs, respectively, applied a technique de- system,” says Paul Callaghan of Victoria parts-per-million shifts needed to access veloped by Pines to compensate for inUniversity of Wellington (New Zealand). chemical information.” “The idea developed by the Berkeley homogeneity to a device developed by During NMR analysis, atoms align group and implemented on a prototype Blümich that uses concentric NdFeB with a homogeneous magnetic field, B0. system in Aachen is very clever and magnets. “We accurately measure the will attract interest in low-field NMR static field and build an rf coil that exA radio frequency (rf ) pulse applied at a applications.” actly matches that field,” says Demas. right angle generates a field, known as According to Eiichi Fukushima of B1, which deflects the alignment. Chem- “By introducing parallel variations in the New Mexico Resonance (a nonprofit rf field, we compensate for the inhomoical information is determined from the corporation), the research is noteworgeneity of the static field.” The result is shift of the precession frequency of the thy. “It spurs the development of equipa “sweet spot” located 7 mm above the atomic spins as atoms return to the iniment that could be used outside the surface of the magnets. tial state. This shift depends on the local laboratory, with possible applications in Varying the length of a B1 pulse genmagnetic field strength and varies according to the chemical environment. erates a spectrum. According to Blümich, fields such as homeland security and environmental monitoring,” he says. a A practical, portable NMR device the trick is to exactly match the static B0 —Steve Miller must use small permanent magnets and rf B1 fields. The team has observed
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