chromatography and qualitative analysis Flashcards
chromatography
separating individual components from a mixture of substances
stationary phase
doesn’t move, solid/ liquid support on a solid
mobile phase
moves, solid/liquid
uses of chromatography
drug analysis, forensic science, air samples
TLC
thin later chromatography
quick, cheap analytical technique
TLC plate
plastic sheet/ glass coated w/thin layer of adsorbent substance- silica
limitations of chromatography
similar compounds have similar Rf values
finding the right solvent book through trail and error
experimental conditions Rf values need to match database values
similarities bw paper and TLC
measure distance traveled as fraction of how far the solvent front has traveled
plate kept in chamber saturated w/solvent
useful for sep pigments
stationary phase of TLC
adsorbent- silica
why is it common to run TLC of sample alongside pure samples of compounds that may be present?
easy to identify amino acid in unknown sample visually w/out needing o calculate any Rf values
what does a high affinity for solvent mean
further distance traveled by pigment
why are there diff Rf value for different substances
each sub has a diff affinity for certain solvent
different adsorption strengths to silica surface
retention time
time taken for a substance to pass through the column
adsorption
solid silica holds diff sub in mixture onto its surface
Rf
retention factor
distance traveled by component/ distance traveled by solvent
why does separation take place?
substances in mixture have diff affinity for the stationary and mobile phase, the more a sub sticks to stationary phase the less distance it travels
draw and annotate steps of TLC
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purpose of watch glass
prevents solvent from evaporating away
purpose of spraying chromatography with locating agents and heating with hair dryer
to show to position of invisible spots
use of gas chromatography
separating and identifying volatile compounds in a mixture
GC stationary phase
high bp liquid adsorbde
alkene
add bromine water
bromine water delcolourises from orange to colourless
haloalkane
add sliver nitrate and ethanol and warm in w.bath(50)
chloroalkane- white ppt
bromoalkane-cream ppt
iodoalkane- yellow ppt
carbonyl 2,4-DNP
orange ppt
aldehyde
tollen’s reagent and warm
silver mirror
primary and secondary alcohol and aldehyde
acidifed potssium dihromate(VI) nd warm in water bath
colour change from orange to green
