Miniature nuclear magnetic resonance spectrometer for in-situ and in-process analysis and monitoring. 1998 annual progress report

Technical Report · Mon Jun 01 00:00:00 EDT 1998

DOI:https://doi.org/10.2172/13464· OSTI ID:13464

Friedman, G; Feinerman, A D

'The purpose of this research project is to develop a miniature Nuclear Magnetic Resonance (NMR) spectrometer. This analytical instrument would potentially be used for in-situ, in-field and in-process monitoring, characterization and identification of various chemical compounds. The intended spectral resolution of the NMR spectrometer is better than 0.1 ppm (parts per million). The development of the miniature NMR spectrometer will rely, in part, on the microfabrication technology that includes photolithography, chemical etching, thin film processing and other techniques originally developed in microelectronics. Miniaturization of the NMR spectrometer will involve the miniaturization of the inductive NMR probes used to pick-up the NMR signals. It will also involve integration of the probe, sample holder and magnetic field correction (shimming) coils into a single miniature system. Lastly, it will involve the development of a hand-held permanent magnet capable of creating magnetic field of over 1 Tesla with uniformity of about 1 part per million over the extent of the sample. The advantage of the developed instrument will not only be its portability, but also its ability to handle nono-liter quantities of fluids. As of today, the following tasks have been completed. (1) Scaled versions (800 micron diameter) of the NMR inductive probes have been designed, fabricated and tested for their radio frequency properties. The resulting probe design, which can be called a scroll coil, has been found to be suitable for further miniaturization and compatible with the existing microfabrication technology. In addition tests and analysis indicate and this design will also provide higher sensitivity to NMR signals per unit volume of the sample than other proposed miniature NMR probes. Analysis and tests of the scroll coil design revealed a surprising fact that the sensitivity of the scroll coil is much better when the conductor thickness is smaller than the conductor skin depth. This result defies the conventional rules of NMR probe design which prescribe that conductors should be thicker than their own skin depth. (2) As samples and NMR probes become smaller, the problem of the NMR spectrum dispersion caused by the mismatch in the magnetic susceptibility of the sample and its surroundings becomes more pronounced. A method and a computer code for numerical modeling of the NMR spectrum dispersion has been developed. Upper bounds on the errors in the spectrum calculation have been derived. The developed numerical techniques have been applied to design NMR probes that introduce as little distortion as possible to the NMR spectrum. These designs rely on passive shimming (magnetic field correction) by specially patterned parts of the coil. (3) Initial evaluation of a commercially available permanent magnet (from Drexel Corporation) capable of delivering a 2 Tesla field has been carried out using numerical modeling.'

• Research Organization: Univ. of Illinois, Chicago, IL (US)
• Sponsoring Organization: USDOE Office of Environmental Management (EM), Office of Science and Risk Policy
• OSTI ID: 13464
• Report Number(s): EMSP-60247-98; ON: DE00013464
• Country of Publication: United States
• Language: English

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