ORGANIC CHEMISTRY- chromatography Flashcards
what are the basic principles of all kinds of chromatography?
A mixture is separated if it is dissolved in a solvent and this mobile phase is passed over a solid ( the stationary phase)
what is the mobile phase?
carries the soluble components of the mixture
what relationship between a sample and the mobile phase makes the sample move faster?
components with more affinity to the solvent move faster
what does the stationary phase do?
Holds back components of the mixture that are attracted to it.
what is the relationship between a sample and the stationary phase that make the sample move slower?
more affinity for the stationary phase means the component moves slower, often attracted by hydrogen bonding
how are substances separated by chromatography?
each component have different affinities to the stationary and mobile phases so they move at different rates and are separated over time.
why will different substances show different Rf values?
they are bonded differently and have different polarities
- more polar bonds = more retention time/ smaller rf value since hydrogen bonds are attracted more strongly to the stationary phase.
what is the stationary phase in TLC?
plate coated in silica SiO2
what are the advantages of TLC over paper chromatography?
runs faster
smaller amounts of mixture can be separated
TLC plates more robust than paper
how can you observe colourless spots?
shine UV light on them
spray with ninhydrin (amino acids from colourless to purple)
what does rf value stand for?
retention factor - measure of the rate of movement of a component
how could you confirm the identity of a substance from its Rf value?
compare your rf value to accepted rf values for that substance
what is column chromatography?
column packed with silica and has solvent run through it downwards
stationary phase in column chromatography?
silica packed into a column
mobile phase in chromatography?
solvent added at top and runs down
called “eluent”
advantages of column chromatography?
more than one eluent can be used which leads to better separation
large amounts can be separated and collected after separation
what is the stationary phase in gas-liquid chromatography?
powder coated with oil packed into long thin capillary tube. Coiled and placed in oven.
mobile phase in gas-liquid chromatography?
carrier inert gas eg He
what do you measure in gas-liquid chromatography?
retention time = diff components of the mixture takes different amounts of time to move through
advantages of GLC?
GC- can detect minute traces of substances
uses of GLC
test athletes blood and urine for drugs
How can you use GC or GCMS to identify substances?
match gas chromatograph to that of a known substance under the same conditions = retention time should exactly match.
substances identity can be confirmed by mass spectrometry, NMR or IR spectroscopy.
how does GCMS work?
gas chromatography is run = retention time recorded.
Mixture run through Mass spectrometer = fragmentation pattern confirms identity.
will alcohol or aldehyde have a shortest retention time by column chromatography?
Aldehyde has shortest retention time = has less polar bond than alcohol so adsorbs less to stationary phase, moving down column quicker rate.
