What is chromatography used for?
- Used to separate and identify components in a mixture.
What are the different types of chromatography?
- Thin Layer Chromatography (TLC.)
- Column chromatography (CC)
- Gas chromatography (GC.)
Set up for TLC.
- Stationary phase plate coated in solid silicon dioxide/ aluminium oxide.
- Solvent moves up the plate.
How can colourless substances be seen using TLC?
- Iodine.
- Ninhydrin
- Fluorescent dyes and UV light.
How can fluorescent dyes/ UV light be used to see colourless compounds on TLC?
- Add fluorescent dye to silicon dioxide/ alumium oxide plate.
- Colourless spots, of compounds, won’t be shown under UV light.
Amino acids are colourless. How are they seen on TLC other than using UV light?
- Place ninhydrin solution on chromatogram.
- Dyes colourless spots purple.
- Position of amino acids seen as purple spots.
What are ninhydrin and UV light described as when identifying amino acids in TLC?
- Developing agents.
What substance, other than ninhydrin, will dye colourless spots in TLC chromatography?
What is this substance called?
- Iodine.
- Called: locating agent.
When do Rf values change?
Different:
- Solvent
- Temperature.
- Solid used on TLC plate.
How do Rf values/ retention times help determine a chemical?
- Compared to library of Rf values/ retention times of known chemicals.
- Ensure done under the same conditions as standards in data book
What does separation of substances depend on in chromatography?
- Balance between solubility in the moving phase and attraction to stantionary phase.
Rf value formula.
distance moved by spot/ distance moved by solvent.
When would you use column chromatography vs TLC?
- Column: when separating LARGER quantities of mixtures.
What is staionary/ mobile phase in column chromatography?
- Stationary: solid silica/ alumina beads.
- mobile phase: solvent passes through top of burette.
What is used to determine compounds in mixtures using column chromatography?
- Different compounds run through column at different rates.
- This means they come out from bottom at different times.
- This is known as: retention time.
What column is often used in column chromatography?
- Burette.
Set up for gas chromatography.
- Stationary phase: column packed with solid OR solid coated by liquid.
- Mobile-phase: high-pressure gas passes through column.
- High temperature.
When is gas chromatography used?
- Separates mixtures of volatile liquids.
How do you identify substances using gas chromatography?
- Use retention times.
- Takes different amount of time for different comounds to travel through the column.
What analytical technique can gas chromatography be combined with?
- Mass Spectrometery.
- Substances are separated using gas chromatography.
- Separated substances run through MS machine to identify the substances.
