Basic Aspects NMR (7) Flashcards
What are the two general types of NMR spectrometer?
wide-line and high resolution
What is wide line used for?
lower power magnets, QC and education
What is high resolution used for?
majority of NMR instruments, signal averaging
What is a CW-NMR spectrometer?
Technique that uses a radiofrequency sweep to excite the Larmor frequencies of the nuclei in the sample; older NMR technique that is not currently widely used.
What is an FT-NMR spectrometer?
uses superconducting magnets to maintain a magnetic field
How do CW and FT NMR spectrometers differ?
The CW spectrometer scans a certain frequency range at a time, whereas the FT-NMR examines all frequencies
Why is FT-NMR the prefered method for acquiring NMR spectra?
allows signal averaging - get greater sensitivity
What are the major components of NMR spectrometers?
stable magnet, transmitter/receiver coil, crystal oscillator, pulse switcher, power amplifier, phase-sensitive detector
How are excitation pulses generated?
crystal oscillator
How is the FID detected?
picked up by transmitter/receiver coil
What are the major types of FT-NMR magnets?
superconducting
Why are superconducting magnets almost exclusively used in modern high resolution NMR?
simple and stable
What are some common magnetic field strengths used in these superconducting magnets?
at or below 4K
Why is homogeneity of the magnetic field strength so important in NMR?
must be kept within ppb limits
What are the 3 main ways that field homogeneity is maintained?
field/frequency lock, shimming, spinning
