Unit 2.8 Instrumental analysis Flashcards
Advantage of instrumental anaylsis?
- Require very small samples:
less damaging or invasive
Important if there is very little of the original to identify - They are quick to carry out
- They give very accurate data
What are the 3 spectrometry’s you’ll be looking at?
- Mass spectrometry
- Infrared spectrometry (IR)
- Nuclear Magnetic Resonance spectroscopy (NMR)
What’s a mass spectrometer?
(3 things)
- An analytical technique
- Used to identify different isotopes
- And find overall relative atomic mass of an element
Explain step 1: Ionisation in mass spectrometry?
(5 things)
- 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 step 2: Acceleration in mass spectrometry?
(2 things)
- Positively charged ions are accelerated towards
- Negatively charged detection plate
Explain step 3: Ion drift in mass spectrometry?
(4 things)
- Ions deflected by magnetic field
- Into a curved path
- Radius of their path dependent on
- Charge & mass of ion
Explain step 4: Detection in mass spectrometry?
(4 things)
- When positive ions hit negatively charged detection plate,
- They gain an electron
- Producing flow of charge
- Greater current produced = greater abundance
Explain step 5: Analysis in mass spectrometry?
(4 things)
- Current values used in combination
- With flight times to produce
- Spectra print-out
- With relative abundance of each isotope displayed
In mass spectrum, why do we see a half traced version of the ion?
(5 things)
- During ionisation process, 2+ charged ion may be produced
- Will 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
In mass spectrum:
What m/z?
What relative abundance?
> _>
- Mass to charge ratio
- Relative atomic mass?
icl i haven’t seen where u had to put a number for a certain bar so i reckon u don’t get fucked up by this one
I changed it lol
For mass spectra graph, how u gain mass for the 2 isotopes
Formula for mass of 2 isotopes:
1(relative abundance x m/z)+2(relative abundance x m/z)/ra1 + ra2
May seem a lil hard to remember but gl bro B)
^ past me said that
Define molecular ion (M+)
The positive ion formed in a mass spectrometer from the whole molecule
Define fragementation
Splitting of molecules in a mass spectrometer into smaller parts
How to identify molecular ions in a mass spectrum?
wait
Describe infrared spectroscopy
- Infrared radiation absorbed by organic molecules
- Causes increased bending and vibrations
- Different bonds absorb different energies
Said to be their characteristic of the bonds and so the absorptions on the spectra can indicate which groups of atoms are present
Energy absorbed in IR spectroscopy measured in wavenumber (units cm-1)
Which parts of a molecule absorb infrared energy?
The bonds
Define wave number
A measure of energy absorbed used in IR spectra
Define characteristic absorption
The wavenumber range at which a particular bond absorbs radiation
How to identify chemical compounds in a IR spectrum?
- U must use the data booklet for the wavenumber as it will guide u to identify bonds within the IR spectrum
- Not based on peaks but based on troughs (the opposite of peaks)
- Be aware of the wave number (must be within range)
Typical ones u should know:
C=O bond - deep trough at 1700
O-H bond - usually within broad trough around 3000
1. After gaining the bonds, gain mr and use ur brain to create the structural formula or molecular formula
An example of an IR spectroscopy?
Breathalysers
Issue with breathalysers against drunk ppl and ketosis?
Both have functional group carbonile bond
However can spot the one who drank too much alcohol:
O-H = carboxylic acid = 2500 - 3550
Describe Nuclear Magnetic Resonance (NMR) Spectroscopy
- Corresponds to the energy required
- To reverse the spin of the nucleus
- Of an atom within a magnetic field
- Causes resonance
- Energy absorbed is shown by chemical shift, δ
Must know how to interpret the spectra of this
An example of an NMR spectroscopy?
MRI scanner ig
How to identify compounds in an NMR spectra?
(might need more work)
- It’s based on environments with n° of protons
- U have data booklet for the chemical shifts
- Number of peaks based on number of environments
- Where they placed based on chemical shift
- Height of peak (frequency) based on number of hydrogens (n° of protons)
If too unsure, still possible to go back
I need to do questions tho
