Mass Spectrometry Flashcards
1
Q
What is structure eludication?
A
- The process of determining the molecular structure of an unknown compound.
2
Q
What are the steps of structure eludication?
A
- Isolate and purify it (precipitation, distillation, recrystallisation, chromatography etc)
- Determine molecular formula (mass spectrometry)
- Identify functional groups and conjugation (infrared and UV/Vis spectroscopies)
- Assemble structural formula with correct bond connectivity and stereochemistry
(NMR spectroscopy)
3
Q
What is Mass spectoscopy?
A
- Mass spectroscopy is a technique that determines the molecular mass of a molecule.
4
Q
Describe the process of mass spectroscopy
A
- Molecules are ionised by impact with electrons in a vacuum
(i.e. turned into charged species – ions) - Some ions fragment to form smaller ions (daughter ions)
- These ions are then accelerated through an electric field
- Ions are separated according to m/z (mass/charge)
– Beam of ions directed into magnetic field, causing ions to bend
– They trace out circular paths, with radii dependant on m and z, but
charge (z) is almost always 1
– Detector measures how far ions have bent, so can work out m
5
Q
What is a molecular ion?
A
- The heaviest possible ion
- results from loss of one electron from the parent molecule
- an electron is so light that the mass of the molecular ion is same as parent molecule (CH3OH)
6
Q
What are daughter ions?
A
- Ions caused after fragmentation
- They can help us determine the structure of a molecule.
7
Q
What is the base peak?
A
- The most intense signal where intensity is set to 100%
8
Q
What is electrospray Ionisation?
A
- Formation of aerosol
- Include mild acid/buffer, so ions formed as MH+ (not M+) i.e. just like protonation
- Ions enter mass analyzer as before
- Very gentle – can use to analyze proteins
9
Q
How do isotopes influence mass spectroscopy?
A
- All isotopes will show up as different lines on the graph. (different ion peaks)
