Chapter 29 - Chromatography and Spectroscopy Flashcards
Why is chromatography used?
to separate indiv components in a mixture of substances
All forms of chromatgraphy?
have a mobile and stationary phase
TLC: stationary phase
either SiO2 (s) or Al2O3 on coat TLC plate. IONIC
TLC: what is the stationary phase held on ?
plastic or Al sheet
TLC: mobile phase?
mixture of solvents
TLC: origin line must be?
- in pencil
* above solvent
TLC: Rf equation?
Retardation factor: distance moved by component/ distance moved by solvent front (always <1)
• depends on the solvents and stationary phase used
TLC: smaller Rf value means?
the component bonds more strongly to the stationary phase (more polar/ charged)
in the developing tank, why is there filter paper?
- filter paper soaked in solvent to saturate the air inside w the solvent
- helps solvent travel against gravity up the plate
to determine which substances are in the compound from a chromatogram ?
look at spots on the same level
can use chromatogram to determine?
purity - only 1 spot
how to visualise spots on a chromatogram - not all are coloured?
- can use UV light/ chemicl stains
- Solvent needs to be evaporated b4
- use iodine chamber
- leave the plate in the chamber for at least 5 mins
- once removed, as the iodine fades the spots’ll become visible
- circle spots w pencil before they fade
how does iodine help to visualise?
- warm beaker so it vaporises- sublimes
* iodine is covalent so can bond to the surface of the components (covalent) so dark brown spots appear
gas chromatography: oven
- regulates temp
- needs to be correct temp - middle of teh BP range
- KEEPS COMPONENTS AS GASES
gas chromatography: gas cylinder
He or N - unreactive mobile phase
gas chromatography: gas flow container valve
- to control the gas flow time through the column
* controls rate at which gas flows thru the column
gas chromatography: sample injection
- if liquid, the sample needs to be heated to vaporise it as it enters the column
- volatile organic chemicals - have to be a gas - GAS C
gas chromatography: recorded and computer
Records the gas chromatogram as a series of peaks - higher peaks = higher quantity
gas chromatography: detector
detects the organic chemicals not N/He. Connected to a computer
gas chromatography: column
- either an oily liquid (alkane) coating the inside of the thin tube/ covering the surface of tiny unreactive beads
- stationary phase
What is gas chromatography used for?
separating volatile organic compounds in a mixture
GC: stationary phase?
oily hydrocarbon (usually long chain alkane) which is held on inert plastic tubing/ inert solid beads in column (usually silica beads)
GC: mobile phase?
unreactive gas - N or noble gas
GC: separation by
solubility in oily hydrocarbon - stationary phase