Quiz 3 Flashcards
what do we study with NMR
the spin in the external magnetic field yields a “net magnetization” (precession) excess, which is parallel to the magnetic field
what is recieved by the receiver antenna
-the RF pulse is sent via the transmitter coil
-the RF energy pulse tilts the net magnetization (precession) into the xy plane
-the net magnetization vector begins to separate into component vectors in the xy plane
-spinning protons emit signals into the receiver coil as they decay back to the z axis
-this is the “NMR signal”
why do different nuclei have different resonance frequencies
-due to shielding effects
what is a shielding effect
the relative density of the electron cloud around each proton position
what are resonance frequencies
the complex mixture of signals
what is plotted on the NMR spectrum
step of what happens to yield an NMR spectrum
resonance frequencies are processed by FT (fourier transformation) and the time domain (frequency of each nuclei) and intensity domains are separated and plotted as NMR spectrum
what is coupling
-the interaction of two or more nearby protons through bonds
-they effect each others spin frequencies
-coupling can be used to produce 2D NMR spectra => the combined (coupled) signals are detected as a crosspeak outside of the diagnol 1D spectrum
what is a cryo-magnet
-where the sample is placed
-superconducting magnets are cooled to low temperatures by liquid helium that has an outer jacket of liquid nitrogen
-the core of the superconducting magnet consists of coil thin wires made of superconducting alloys
-the coil (magnet) and the coolants are insulated in container with vacuum chamber around the liquid jackets
precession
motion of spinning charged particle in an external magnetic field (similar to that of a spinning gyroscope in gravitation field)
what is an RF pulse
large range of frequencies is excited by a short pulse of RF energy around a centered carrier frequency (resonance frequency)
what is an FID
-free induction decay
-contains all the frequency and intensity information for each of the unique populations of nuclei in the sample
what do the crosspeaks tell you in 2D NMR
-where there is a relationship
-the coupling correlations of nearby nuclei
ppm
-resulting frequency differences from shielding are reported in ppm
MRI and how is it applied
-MRI uses intact samples and applies complex temporal and spatial variations in sampling to generate 2D and 3D image of the sample
-applied:
*frozen foods to track freezing process
*composition of pastes and sauces
*analysis of cooked products
*can also determine if fruits are used for juice or fresh
relaxometry and its uses
-times associated with the relaxation of water protons
-yields info about the association of water with the macromolecules in a sample
-as macromolescules increase, the relaxation time of the water protons increases
-used of dissolution process of powder ingredient in water
