Quiz 3 Flashcards

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1
Q

what do we study with NMR

A

the spin in the external magnetic field yields a “net magnetization” (precession) excess, which is parallel to the magnetic field

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2
Q

what is recieved by the receiver antenna

A

-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”

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3
Q

why do different nuclei have different resonance frequencies

A

-due to shielding effects

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4
Q

what is a shielding effect

A

the relative density of the electron cloud around each proton position

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5
Q

what are resonance frequencies

A

the complex mixture of signals

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6
Q

what is plotted on the NMR spectrum

step of what happens to yield an NMR spectrum

A

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

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7
Q

what is coupling

A

-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

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8
Q

what is a cryo-magnet

A

-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

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9
Q

precession

A

motion of spinning charged particle in an external magnetic field (similar to that of a spinning gyroscope in gravitation field)

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10
Q

what is an RF pulse

A

large range of frequencies is excited by a short pulse of RF energy around a centered carrier frequency (resonance frequency)

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11
Q

what is an FID

A

-free induction decay
-contains all the frequency and intensity information for each of the unique populations of nuclei in the sample

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12
Q

what do the crosspeaks tell you in 2D NMR

A

-where there is a relationship
-the coupling correlations of nearby nuclei

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13
Q

ppm

A

-resulting frequency differences from shielding are reported in ppm

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14
Q

MRI and how is it applied

A

-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

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15
Q

relaxometry and its uses

A

-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

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