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NMR_Inst_2010 - NMR Instrumentation BCMB/CHEM 8190...

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NMR Instrumentation BCMB/CHEM 8190 Biomolecular NMR
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Instrumental Considerations - Block Diagram of an NMR Spectrometer B 0 Magnet Probe Lock Receiver Transmit Computer Sample
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Modern NMR Magnets are Super Conducting Solenoids Materials: NbTi < 10T, NbSn > 10T Max Field (2000): 23.5 T (900 MHz) Advantages: high field, stability, homogeneity > 1 : 10 9 B 0 i
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Shim Coils B 0 Z Inherent field profile B 0 (z) = B 0 + a1 z + a2 z 2 + …. Design coils to produce –a1 z, -a2 z 2 , etc ai are set by adjusting current in each of 16-40 coil sets – x, y, z, powers and cross terms i i z a linear z coil
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Room Temperature Shim Assemblies From Modern NMR Techniques for Chemistry Research , Andrew E. Derome
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Shimming Origin: old electromagnets used shims under pole pieces Interactive shimming B 0 Z ν 0 Auto shim: - based on amplitude of lock signal Gradient shim: observing effect of imposed field gradient – can deconvolute field inhomogeniety Adjust z 2
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A Deuterium Lock Stabilizes the Field X axis (absorptive) Y axis (dispersive) ω 0 ω 0 Drift of field will produce positive and negative signals Depending on direction when dispersive signal is observed
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