Topic 19 Anaylytical Techniques Flashcards
What is a use for NMR spectroscopy in medicine?
MRI scan
State the region of electromagnetic spectrum used in 1H NMR spectroscopy
Radiowaves
Explain why CDCl3 is used as a solvent in 1H NMR spectroscopy.
No H atoms
How to determine the number of H/C environments from NMR spectrum? (Low res)
Number of peaks = number of environments
How to work out how many subpeaks there would be in a 1H NMR in High resolution?
(number of adjacent H atoms) + 1 rule
What does NMR stand for?
Nuclear Magnetic Resonance
What are nucleons?
proton + neutrons (things in nucleus)
What is multiplicity? How to name them?
The number of symmetrical peaks in High res NMR
singlet, doublet, triplet, quartet, quintet… or multiplet of 6 so on
Is there high resolution NMR for 13C and 1H?
No for 13C
Yes for 1H
What is chromatography used for?
Seperation
What are the types of chromatography (in spec)?
- gas chromatography
- HPLC
- TLC
How does chromatography generally work?
2 phases: mobile phase and stationary phase
Since molecules have ‘an affinity’ for either phase
The retention time often helps identify
Why do molecules have an affinity for mobile or stationary phases in chromatography?
Relevant IMFs
What is the stationary phase of chromatography often made of?
Silica
it is polar
What does the retention time say about the component in a mixture?
more polar = higher affinity to polar Silica in stationary phase
= retarded = higher retention time
How does gas chromatography work?
- inert carrier gas (mobile phase) in cylinder
- pump allows sample inlet
- long column lined with Silica as stationary phase - in oven
to reach detection
Do polar or nonpolar molecules take longer to get detected?
Polar
as have higher affinity to polar stationary phase
What is retention time?
Time taken for samples to elute from the column
What is HLPC?
High Performance Liquid Chromatography
- separate liquid/aqueous mixtures
How does HLPC work?
- Add mobile phase solvent to cover all silica beads
- add test mixture to top of column
- keep adding solvent to have constant supply of mobile phase
- collect all eluted substances and test
What is TLC? What is it made of?
Thin Layer Chromatography
Silica!
How to do TLC?
- scratch a line on the paper
- dip in solvent (mobile phase)
- allow run
- draw solvent front line
- calculate Rf value
What does the movement of TLC indicate?
- no movement = insoluble
- closer to start line = higher affinity for stationary phase
- further from start line = higher affinity for mobile phase
How to do chromatography for α amino acids?
Dip one side in solvent 1
rotate 90°
Dip in solvent B
- separation after solvent 1 does not indicate number of amino acids present
What do 13C NMR peaks indicate?
number of carbon environments
but proportion not representative of ratio of number of carbons in each environment
How to choose suitable solvent for recrystallisation?
Soluble in hot solvent and insoluble in cold solvent
