Nuclear Magnetic Resonance and Magnetic Resonance Imaging for Process Analysis
Process Instrumental Methods
Published Online: 15 SEP 2006
Copyright © 2000 John Wiley & Sons, Ltd. All rights reserved.
Encyclopedia of Analytical Chemistry
How to Cite
McCarthy, M. J. and Bobroff, S. 2006. Nuclear Magnetic Resonance and Magnetic Resonance Imaging for Process Analysis. Encyclopedia of Analytical Chemistry. .
- Published Online: 15 SEP 2006
Nuclear magnetic resonance (NMR) spectroscopy is an experimental technique based on the interaction between nuclear magnetic moments and an applied magnetic field. The nuclei emit and absorb energy at a specific frequency that is proportional to the applied magnetic field. Magnetic resonance imaging (MRI) is the term used to describe the spatial resolution of NMR signals within a sample. NMR/MRI may provide information on the weight, chemical composition, physical properties, and structure of a sample. NMR is a noncontacting and noninvasive measurement. NMR and MRI are suitable for use in process control and have been applied to polymer processing, food processing and refinery processes. The response is linear from the detection limits of approximately 10 ppb to 100%. The accuracy of the technique depends on the signal-to-noise ratio (S/N), which is a function of the sample size, applied magnetic field strength, the radio-frequency (rf) coil and the spectrometer hardware. Typical accuracy of the technique is 0.5% for measurements of composition and 1–5% for viscosity. NMR cannot generally be applied to magnetic or highly conductive materials.