Thin Layer Chromatography UPDATED
Exam Questions and CORRECT Answers
What level should the solvent be in the developing chamber? - CORRECT ANSWER -
Solvent must be below the spotting line so that solvent does not dissolve samples on the spotting
line.
Why is it suggested that one uses tweezers to place the TLC plate in the developing chamber? -
CORRECT ANSWER - Oils from you fingers can sometimes smear or ruin a TLC plate.
Why must the bottom of the TLC plate be level with the bottom of the developing chamber? -
CORRECT ANSWER - If not, then solvent will rise up unevenly on the TLC plate.
What effect might moving or jostling the developing chamber during the developing stage have
on the rising of the solvent? - CORRECT ANSWER -
Why must the developing chamber be covered? - CORRECT ANSWER - Make sure the
top is placed back on so the solvent does not evaporate.
Evaporation of the solvent during this stage causes the development of the TLC plates to be
messy and ineffective.
Before developing a new TLC plate, why do you need to add solvent to 4mm height? -
CORRECT ANSWER - Ensure you have enough solvent for complete development, so
that solvent reaches determined solvent front.
Why do you have to make sure solvent does not rise up past solvent front (5mm)? - CORRECT
ANSWER - If it does, spots in visualization stage will be difficult to evaluate. Rf will be
too high.
Why do you need a filter paper in the developing chamber? - CORRECT ANSWER - To
saturate developing chamber with solvent vapors, facilitates capillary action.
, Why must you avoid leaning plate against filter paper? - CORRECT ANSWER - Eluent
on the filter paper can be absorbed by adsorbent and interfere with ascending eluent.
Where should the solvent come from? - CORRECT ANSWER - The bottom, not the sides.
This extra eluent may prevent the compounds traveling from moving up the plate in a straight
line.
What must you draw lines lightly on TLC plate? - CORRECT ANSWER - To not flake of
adsorbent
if flaked, a gap might form that may stop the flow of the eluent or cause eluent to run crookedly.
Why is a pencil always used to mark a plate? Why is ink never used to mark a plate? -
CORRECT ANSWER - Graphite (carbon) is inert, will not chromatograph.
Ink will chromatograph, interfering with the samples and giving flawed results.
What happens if you don't allow the solvent to dry completely between applications to the same
spot? - CORRECT ANSWER - The spot will become too large, leading to 2 or more spots
of a sample to possibly overlap. This causes erroneous conclusions about the separation and/or
the sample's purity or content.
What problem could streaking spots lead to? - CORRECT ANSWER - streaking may lead
to the overlap of two or more compounds, thus skewing results
...
What happens if a sample contains too many components? - CORRECT ANSWER - Spots
may just run together and appear as a streak.
Exam Questions and CORRECT Answers
What level should the solvent be in the developing chamber? - CORRECT ANSWER -
Solvent must be below the spotting line so that solvent does not dissolve samples on the spotting
line.
Why is it suggested that one uses tweezers to place the TLC plate in the developing chamber? -
CORRECT ANSWER - Oils from you fingers can sometimes smear or ruin a TLC plate.
Why must the bottom of the TLC plate be level with the bottom of the developing chamber? -
CORRECT ANSWER - If not, then solvent will rise up unevenly on the TLC plate.
What effect might moving or jostling the developing chamber during the developing stage have
on the rising of the solvent? - CORRECT ANSWER -
Why must the developing chamber be covered? - CORRECT ANSWER - Make sure the
top is placed back on so the solvent does not evaporate.
Evaporation of the solvent during this stage causes the development of the TLC plates to be
messy and ineffective.
Before developing a new TLC plate, why do you need to add solvent to 4mm height? -
CORRECT ANSWER - Ensure you have enough solvent for complete development, so
that solvent reaches determined solvent front.
Why do you have to make sure solvent does not rise up past solvent front (5mm)? - CORRECT
ANSWER - If it does, spots in visualization stage will be difficult to evaluate. Rf will be
too high.
Why do you need a filter paper in the developing chamber? - CORRECT ANSWER - To
saturate developing chamber with solvent vapors, facilitates capillary action.
, Why must you avoid leaning plate against filter paper? - CORRECT ANSWER - Eluent
on the filter paper can be absorbed by adsorbent and interfere with ascending eluent.
Where should the solvent come from? - CORRECT ANSWER - The bottom, not the sides.
This extra eluent may prevent the compounds traveling from moving up the plate in a straight
line.
What must you draw lines lightly on TLC plate? - CORRECT ANSWER - To not flake of
adsorbent
if flaked, a gap might form that may stop the flow of the eluent or cause eluent to run crookedly.
Why is a pencil always used to mark a plate? Why is ink never used to mark a plate? -
CORRECT ANSWER - Graphite (carbon) is inert, will not chromatograph.
Ink will chromatograph, interfering with the samples and giving flawed results.
What happens if you don't allow the solvent to dry completely between applications to the same
spot? - CORRECT ANSWER - The spot will become too large, leading to 2 or more spots
of a sample to possibly overlap. This causes erroneous conclusions about the separation and/or
the sample's purity or content.
What problem could streaking spots lead to? - CORRECT ANSWER - streaking may lead
to the overlap of two or more compounds, thus skewing results
...
What happens if a sample contains too many components? - CORRECT ANSWER - Spots
may just run together and appear as a streak.
