C Unit 2.8 Instrumental Analysis Revamp Flashcards
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…
Define characteristic absorption?
(2-way)
- The wave number range at which
- a particular bond absorbs radiation
Within infra-red spectrum of a molecule, what’s the right hand side area called?
(3 things…. bro u’ll probably only need to know it’s name…)
- The fingerprint region
- Specific to the molecule
- Whole spectrum can be compared with known samples using a database….?
Within infra-red spectrum of a molecule, how to tell if a certain bond is rlly in there?
…. based on the trough being there… broadness also showing like wavenumber range….
But, what can we mostly gain from analysing an infra-red spectrum of a molecule?
(3 things)
- Functional groups present
- Possible type of compound
- Certain structural features
2 examples of infrared spectroscopy being used?
- Breathalysers
- Global warming
Issue with breathalysers against drunk people and people suffering from ketosis?
Solution perhaps?
(3-way)
- Both have function group -C=O
- But can spot one who drank too much alcohol:
- O-H carboxylic, definitely not ketones
NMR spectroscopy…. NMR means what?
Nuclear Magnetic Resonance
Explain NMR spectroscopy?
(3-way + 2-way)
- Corresponds to the energy required
- to reverse spin of nucleus
- of an atom within magnetic field
- Causes resonance
- E absorbed shown by chemical shift (δ)
What’s an example of NMR spectroscopy?
MRI scanner :b
What are 2 types of NMR spectroscopy to of our concern?
(Each provide their own table in data sheet ,’:0)
- 13C NMR spectroscopy
- 1H NMR spectroscopy (low resolution… no singlet n stuff das A2)
Explain 13C NMR spectroscopy?
(2 things + 2-way)
- Focuses on carbon environments in a molecule
- C-13 = naturally abundant ∴ weaker signals than 1H NMR spectroscopy
- The chemical shift tells us the type of carbon present
- ;different functional groups give different peaks
What can the peak height be based on in 13C NMR spectroscopy?
Can there be the same bond with different δ?
Number of same molecules (n° of the same environment).
… Yes, remember when i said different functional groups give different peaks?
Explain 1H NMR spectroscopy (low resolution)?
(4 points)
- Focuses on hydrogen (proton) environments in a molecule
- n° of peaks = n° of environments
- Height of peak = n° of H in environment
- Be aware whether it’s 1 whole environment or actually just 2 (Any example?)
Tell me about the δ values in 1H NMR spectroscopy (low resolution)?
(2 things)
- Values vary within the ranges stated in data sheet
- E.g. -O-H has quite a big range (1.0 - 5.5)
This one is mostly a big heads up on questions, the true applying knowledge. Ig I have my book but still.
Congrats
