C Unit 2.8 Instrumental Analysis Revamp Flashcards
(39 cards)
The 3 spectrometry to of our concerns?
- Mass spectrometry
- IR spectrometry
- NMR spectrometry
What’s mass spectrometry?
(3-way)
- An analytical technique
- used to identify different isotopes
- and find overall relative atomic mass of an element
What are the 5 stages within mass spectrometry?
Stage 1: Ionisation
Stage 2: Acceleration
Stage 3: Ion drift
Stage 4: Detection
Stage 5: Analysis
Explain stage 1: Ionisation?
(2-way + 3-way)
- A sample of an element is vapourised and injected
- into mass spectrometer
- Where high voltage passed over chamber
- causes electrons to be removed from atoms (ionised)
- leaving 1+ charged ions in chamber
Explain stage 2: Acceleration?
(2-way)
- Positively charged ions are accelerated towards
- negatively charged detection plate
Explain stage 3: Ion drift?
(2-way + 2-way)
- Ions deflected by magnetic field
- into a curved path
- Radius of their path dependent on
- charge & mass of ion
Explain stage 4: Detection?
(3-way + 1… way)
- When positive ions hit negatively charged detection plate,
- they gain an electron
- , producing flow of charge
- Greater current produced = greater abundance
Explain stage 5: Analysis?
(3-way + one. way)
- Current values used in combination
- with flight times to produce
- a spectra print-out
- With relative abundance of each isotope displayed
In mass spectrum (probably the graph?), why do we see a half traced version of the ion?
(3-way + 2 things)
- During ionisation process, 2+ charged ion may be produced
- which’ll be affected more by magnetic field
- producing curved path of a smaller radius
- As a result, mass to charge ratio (m/z) is halved
- Can be seen on spectra as a trace at half the expected m/z value
What’s m/z?
What’s relative abundance? (<_<)
(Mass spectrometry)
- Mass to charge ratio
- …. Ig it’s how much of the ion there is? Consider the fact that u gain their isotopes in the spectra sooo…. yea….
How to calculate RelativeAtomicMass of elements from mass spectra?
The formula:
1(relative abundance x m/z)+2(relative abundance x m/z)/ra1 + ra2
1 & 2 meaning the isotopes.
There’s 2 isotopes with relative isotopic masses of 35 & 37.
One with 35 has RA of 3
One with 37 has RA of 1
Calculate the RAM of the element?
((35x3) + (37x1))/3+1
= 35.5
(There’s a different method in the actual booklet, I took the one from 1.3 O_o)
Define molecular ion (M+)
(2-way)
- The positive ion formed in a mass spectrometer
- from the whole molecule
How is a molecular ion gained from within mass spectrometry?
(2-way + 1-way)
(Could it be optional…?)
- Molecules introduced into mass spectrometer
- bombarded by high energy electrons
- Knocks off electrons leaving M+
Define fragmentation?
(2-way)
(Ig it speaks for itself anyway)
- Splitting of molecules in a mass spectrometer
- into smaller parts
In mass spectra, how to find out the molecules Mr?
(2 points)
- The highest m/z
- That’s also its molecular ion
Hence, in mass spectra, how to identify the structure?
(5, thought provoking, must observe,-way)
- First know Mr
- Given fragment table otherwise:
- OH = 17
- CH3 = 15, CH3CH2 = 29
- All about ur judgement
In mass spectra, do we care about the height of the bars for the molecule?
… NO.
How to truly tell if the molecule in mass spectra is an alcohol?
If there’s a peat at 17
Concluding… what are the 4 things we can gain from mass spectrometry?
(2 of em with () )
- Molecular mass (M+)
- Molecular formula
- Structural features (fragmentation)
- Presence of halogens
What’s infrared spectroscopy?
(4-way)
- An analytical technique (<_<… again)
- to identify & analyse substances
- by measuring how they absorb IR light
- which causes molecular vibrations
Meaning of “different bonds absorb different energies” in IR spectroscopy?
(1 + 2-way)
- Said to be the characteristic of the bonds
- The absorptions on the spectra can indicate
- which groups of atoms are present
Measurement of energy absorbed in IR spectroscopy?
Wavenumbers
(cm-1)
Which parts of a molecule absorb infrared energy?
The bonds…
