Forensic Applications of Mass Spectroscopy
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Name some of the forensic applications of mass spectroscopy.
- Drug Analysis (cocaine, hash, LSD)
- Toxicology (poisons, alcohol, mace)
- Arson (petroleum, alcohol based ignitable liquids)
- Explosives (nitro-substituted benzenes, TATP)
- Trace Analysis (polymers, adhesives, general unknowns)
What is a mass spectrometer?
An analytical instrument which creates charged particles from molecules, separate ions, and detect ions.
A mass spectrometer separates ions according to which ratio?
mass to charge (m/z)
What are the 2 gas-phase methods of ionization?
- Electron Impact
- Chemical Ionization
What are the 2 spray methods of ionization?
- Atmospheric Pressure Chemical Ionization
What are the 2 desorption methods of ionization?
- Fast Atom Bombardment
- Matrix-Assisted Laser Desorption Ionization
How is the molecular ion formed in electron-impact?
it is the result of a high energy electron colliding with a molecule forcing the loss of an electron from the molecule
T/F: Molecular ions may degrade further to smaller fragment ions as a result of residual energy from the electron impact process.
______ of the filament in the source causes the emission f electrons which are accelerated towards the anode in the ______ ______ ionization technique.
Name some of the advantages of electron impact.
- Fragmentation libraries exist
- Interface to GC
- Non-Polar Samples
Name some of the disadvantages of Electron Impact.
- Parent Identification
- Need volatile sample
- Need thermal sample
- Low mass compounds (<1000 amu)
an atom or group of atoms that has at least one unpaired electron and is therefore unstable and highly reactive
a particle that has neither positive nor negative electric charge; a net electric charge of zero
an ion or group of ions having a positive charge and characteristically moving toward the negative electrode in electrolysis; even electron species
Define radical ion
a charged compound that has an unpaired electron; it may be either a radical cation or radical anion; odd electron species
What is the most common and simplest fragmentation?
bond cleavage resulting in neutral radicals and a cation
What is the less common fragmentation type?
An even-electron neutral is lost and results in odd-electron radical cation fragment ion
What is heteroatom participation?
the presence of a functional group containing a heteroatom (N, S, O, X) can alter the fragmentation pattern
Between what 2 things do the ion molecule reactions occur in chemical ionization?
- ionized reagent gas molecules
- volatile analyte neutral molecules
In positive ion mode of chemical ionization, is a proton added or subtracted?
What are the advantages of the chemical ionization technique?
- parent ion presence
- interface to GC
What are the disadvantages of the chemical ionization technique?
- no fragment library
- need volatile sample
- need thermal stability
- low mass compounds (<1000 amu)
What is the nitrogen rule?
Ions without N atoms or those with an even number of N atoms have an even numbered mass, and the majority of the fragment ions have odd masses.
Ions with an odd number of N atoms have an odd numbered mass and the majority of the fragment ions have even masses.
T/F: The presence of bromine or chlorine in a molecule or ion are not easily detected by the intensity ratios of ions differing by 2 amu.
False! They can be easily detected by the intensity ratios differing by 2 amu.
What 2 ions are included in the 50:50 mixture of bromine?
79Br and 81Br
What 2 ions are included in the 75:25 mixture of chlorine?
35Cl and 37Cl
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