Pulse nuclear magnetic resonance detection

The microwave detected MODR scheme closely resembles pulsed nuclear magnetic resonance (Hahn, 1950), optical coherent transients by Stark switching (Brewer and Shoemaker, 1971) and laser frequency switching (Brewer and Genack, 1976). The on-resonance microwave radiation field, ojq = ( 2 — Ei)/H, creates an oscillating bulk electric dipole polarization (off-diagonal element of the density matrix, pi2(t)). The oscillation is at u>o u>r, where ojr is the (Mj-dependent) Rabi frequency,... 

Nuclear magnetic resonance (NMR) can be used as a rapid alternative to differential scanning calorimetry in the determination of the solid fat content and studies on the melting behaviour. The determination is based on detection of the different populations of protons in solid and liquid phases, which indicates the hardness of the fat. Hernandez and Rutledge (1994b) used low resolution pulse NMR to compare melting curves of roasted and non-roasted cocoa butters from Africa, Indonesia and South America. Discriminant analysis techniques showed... 

Methods that utilized derivatives (DNP and 7-hydroxyquinoline) combined with colorimetric or fluorimetric detection were not specific for acrolein and consistently did not correlate with those obtained from bioassays. Certain direct methods of detection (nuclear magnetic resonance (NMR), fluorescence, and differential pulse polarography) gave the best correlation to the bioassay results (see discussion of analysis of environmental samples in Section 6.2). 

Nuclear magnetic resonance (NMR) spectrometers offer spectral capabilities to elucidate polymeric structures. This approach can be used to perform experiments to determine comonomer sequence distributions of polymer products. Furthermore, the NMR can be equipped with pulsed-liied gradient technology (PFG-NMR), which not only allows one to determine self-diffusion coefficients of molecules to better understand complexation mechanisms between a chemical and certain polymers, but also can reduce experimental time for acquiring NMR data. Some NMR instruments can be equipped with a microprobe to be able to detect microgram quantities of samples for analysis. This probe has proven quite useful in GPC/NMR studies on polymers. Examples include both comonomer concentration and sequence distribution for copolymers across their respective molecular-weight distributions and chemical compositions. The GPC interface can also be used on an HPLC, permitting LC-NMR analysis to be performed too. Solid-state accessories also make it possible to study cross-linked polymers by NMR. 

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