W8 Mass Spectromotry Flashcards
What is mass spectrometry
Mass spectrometry is an analytical technique
that involves the ionisation of chemical species
then sorting of the ions based on their mass to charge ratio
What are the main things it is used for
Obtaining details about
- mass of a chemical species
- structural information about molecules
What are advanced ms techniques used for
analyze complex mixtures including ones which contain biomolecules e.g. carbohydrates or proteins
What are the 3 main areas mass spectrometry is used
biomolecule characterization
environmental analysis
forensic analysis/clinical
What is a Dalton
one unit of mass and is defined as 1/12th the mass of a single carbon 12 atom
What is an isotopologues
it is a molecule that differs only in isotopic composition
How does the size of a molecule affect its chance to have a less abundant isotope
the larger the molecule the chance to have more than one atom of a less abundant isotope is higher
What is a characteristic of Isotopologues on a graph
peak splitting
What are the main components of a mass spectrometre
the machines consist of
an ion source
mass analyzer
detector
What is the 1st step an ms follows
the sample is vaporised and ionised
what is the 2nd step an ms follows
ions subject to a filter to separate them according to their mass to charge ratio
what is the 3rd step an ms follows
the stream of mass separated ions are detected
what is the 4th step an ms follows
an electrical output is generated producing a plot of the signal intensity for each mass to charge ratio.
What are the steps an ms follows
the sample is vaporised and ionised
ions subject to a filter to separate them according to their mass to charge ratio
the stream of mass separated ions are detected
an electrical output is generated producing a plot of the signal intensity for each mass to charge ratio.
What is the highest peak in a ms known as
base peak
what is a base peak
it is the highest peak in a ms and is set to 100% relative intensity
What is a molecular ion peak
the signal that represents the mass of the target compound
what is the units of the x axis in ms
Mass / Charge (M/Z)
Why are there many peaks on the mass spec
there are many peaks as they are the fragments of the molecule
What are the two main types of mass spectrometry techniques
Electron Impact Ionization (EI)
Matrix assisted laser desorption ionisation (MALDI)
What happens in Electron Impact Ionization
The vaporized sample gets bombarded with high energy electrons causing an electron from the compound to be ejected.
This makes the compound a high energy charged species,
which can then breakdown into lower weight fragment ions and radicals
What is the first step of EI MS
Sample vaporised and ionised
What is the second step of EI MS
Ions accelerated in an electric field
What is the third step of EI MS
In the magnetic sector circular flight path adopted dependent upon the mass to charge ratio
What is the fourth step of EI MS
Changing magnetic field strength allows only ions of correct M/Z ratio through the detector
What is the fifth step of EI MS
Spectrometer operates by sweeping the magnetic field to scan hte mass range
What is the process of EI MS (Simplefied)
Sample Vaporized and Ionized
Ions accelerated
Circular flight path can be adopted dependent of mass to charge ratio
change in magnetic field allows what we want to be detected
spectrometer scans magnetic field for mass range
what can explain fragments
homolyic alpha cleavage
heterolytic alpha cleave
these are both pathways that can explain
What does homolytic alpha cleave often do
it often gives the most abundant ion
the radical is often used to form a double bond with the heteroatom
loss of the largest possible radical favoured
What can we get in addition to fargmentation
we can also get rearrangements
what is the mclafferty rearrangement
It is a process which can be undertaken by
aliphatic ketones
aldehydes that feature gamma hydrogens
(Must have at least alkyl chain of three carbons)
carboxylic acids
esters
amides
Describe Maldi MS
softer low energy ionisation technique
what happens to the sample in Maldi MS
mixed with a matrix compound that is a strong uv absorber
why is the sample mixed with a strong uv absorber matrix
its function is to absorb energy from a pulsed ultraviolet laser and transfers it to the sample
