29. Chromatography And Spectroscopy Flashcards
What are the two phases of chromotography?
Stationary phase
Mobile phase
What does chromatography do?
Seperate individual components from a mixture of substances
What is the stationary phase (chromatography)
No movement
Normally a solid of liquid supported by a solid
What is the mobile phase (chromatography)?
Moving phase
Normally a liquid or gas
What applciations can chromatography be used for?
Drug analysis
Air samples
Forensic science
What is thin layer chromatography?
A quick and inexpensive method of chromatography that indicates how many components are in a mixture
What is the TLC plate made up of (chromatography)
Plastic or glass sheet coated w a thin layer of solid adsorbent substance-usually silica
What adsorbent substance is usually used in TLC?
Silica gel
What is the adsorbtion process in TLC?
The solid silica holds the different substances in the mixture to its surface
How does seperation occur in TLC?
The different components have different affinities for the adsorbent so bind with different strengths to its surface
Describe the steps to carry out TLC
- Draw the base line on TLC plate 1cm away from end
- Use capalliary tube to spot small amount of soloution of sample on base line
- Place in either beaker w 0.5cm of solvent in and a watch glass on top / or use TLC tank
- Allow solvent to rise until 1cm from top and immediately remove and mark solvent front
- Allow to dry and circle spots
What must we use to mark base line in TLC and why?
Pencil, insoluble so wont interfere with mobile phase
What must we ensurewhne placing TLC plate in beaker and why?
that the solvent is under base line so sample doesnt dissolve in solvent soloution
What can we do if spots appear invisible in TLC?
Shine UV light
Spray w iodine
How do we interpret TLC results?
Each Component can be identified by Comparing retention factor values (Rf) with known values recorded for the same solvent and adsorbant
Whats the formula to calculate retention factor values?
Rf=distance moved by component/distance moved by solvent front
How can we compare samples visually?
Run pure samples of compounds that might be present along side unknown sample
What is gas chromotography?
Used to seperate and identify volatile organic compounds present in a mixture
What is the stationary phase in GC?
High boiling liquid adorbed onto an inert solid support
What is the mobile phase in GC
Non réactive carrier gas such as helium or neon
How does GC work?
- Volitile mixture injected into gas chromatograph
- moblie carrier carries sample through the capillary collumn which contains stationary phase
- the more soluble a component is the more it interacts with liquid stationary phase so the slower it moves
- this means components are sperated by solubility and reach detector at different retention times
How can we identify components from retention times (GC)?
Compare to retention times for known components
What does the area under a retention time peak tell us (GC)?
Peak intergrations can tell us the concentrations of componenents
How do we determine concentration of a sample from its peak intergration?
- standard soloution of known concs of compound being investigated
- obtain gas chromatographs for each standard soloution
- plot calibration curve of peak area against concentration (external calibration)
- use callibration curve to measure conc of compound being investigated
