Mass Spectrometry Flashcards
NMR continued, MRI and Mass Spectometry
Frequency on NMR Spectrum shows…..
The extent of shielding of the electrons and the electron density.
More electron density (shielding) leads to lower frequencies, while less electron density (deshielding) leads to higher frequencies.
On the x-axis of an NMR Spectrum the numbers go in the opposite direction.
T/F
True
The intensity of the signal/peak on NMR Spectrum tells….
How many protons or hydrogens are giving the signal.
Both height and width (AUC) of the peaks on NMR Spectrum gives intensity.
T/F
True
What is MRI?
How does it relate to NMR?
How is the image created?
(Magnetic Resonance Imaging) is a form of NMR that focuses on hydrogen nuclei (protons) in water (H₂O) molecules, particularly in biological tissues..
The concentration of water in soft tissue vs in bone creates the contrast in the scan.
Explain Mass Spectrometry.
What happens when you place a positive charge in a magnetic field?
How does it identify a compound?
When you place a positive charge in a magnetic field, it deflects.
How much it deflects depends on
1) Strength of the magnetic field (B)
2) Charge (Q)
3) Mass (lighter is deflected more)
Calculating how much is deflects gives the mass of the molecule which can identify the compound.
Explain Mass Spectrometry.
What are the requirements or the set up for Mass Spectrometry.
1) strong vacuum
(circular in shape since corners are weak spots)
2) Electrodes
(one positive and one negative to allow the proton to moves towards the negative electrode)
3) Ionization must occur
Real life examples of Mass Spectrometry.
1) Soft X-ray at airport
2) Puff of air used to find trace amounts of drugs. (fentanyl and cocaine)
What are the ionization techniques of Mass Spectrometry.
Remember these refer to the ways in which to generate ions.
1) EIMS
2) CIMS
3) FABMS
4) ESIMS
5) ICPMS
6) MALDIMS
EIMS
How does it ionize an electron?
How can this be used to identify a molecule?
Electron Impact Ionization Mass Spectrometry.
The coil of wire is heated in a vacuum connected to a power supply to allow electron emission.
The hot excited electron absorbs energy, stops orbiting and leaves.
The beam of electrons is directed to a gas stream and ionizes the gas molecules. A particular molecule will always give a characteristic molecular fragment pattern.
So check the pattern of the smallest fragments
Splitting molecules A and B may give similar fragments but different proportion.
CIMS
Chemical Ionization Mass Spectrometry
Uses reagent gas/small molecules that react with parent instead of an electron beam.
It is softer than EIMS as it doesn’t blow the molecules into small fragments and isn’t disintegrated completely.
You instead get larger fragments.
FABMS
Fast Atom Bombardment Mass Spectrometry
A fast atom such as an inert, stable, heavy gas atom ( Xe, Ar, Ne, He, Kr, Rn) causes fragmentation. Since it is inert it doesn’t affect analysis. To analyze read the fragmentation pattern.
It is called fast because under normal circumstances Xenon molecules are relatively slow, so it is sped up to cause fragmentation upon collision.
ESIMS
Electrospray Ionization Mass Spectrometry.
The charged metal tip of a syringe nozzle is used to release a charged droplet. The volatile solvent evaporates so the droplet decreases in size and becomes more concentrated until individual molecules develop a charge.
This doesn’t cause fragmentation so the molecule remains intact.
Thus it is very effective to analyze large proteins since they don’t have to break into millions of fragments.
ICPMS
Inductively Coupled Plasma Mass Spectrometry
High energy induction heating causes ionization then it is sent to Mass Spectrometry.
Used to analyze materials with heavy metal complexes.
Fragmentation occurs.
MALDIMS
Matrix Assisted Laser Desorption Ionization Mass Spectrometry
Dissolve sample in matrix. This absorbs the frequency and the colour of the laser. Then use laser to liberate molecules from the matrix. Molecules vaporize from the matrix and a proton jumps off.
Solvent dissolves and the main analyte is analyzed.
Soft ionization and the molecule remains intact.
Terms related to Mass Spectrometry.
1) GCMS
2) LCMS
3) HPLCMS
4) TOF
1) Gas Chromatography Mass Spectrometry
(Gas chromatography was first used to separate mixture, then use mass spectrometry for analysis)
2) Liquid Chromatography Mass Spectrometry
3) High Pressure Liquid Chromatography Mass Spectrometry
or it is High Performance
4) Time-of-Flight Mass Spectrometry
