in thin layer chromatography aspirin and caffeine were used as spot. under uv light they appear as dark dots. why do they appear as dark dots? but aspirin is a fluorescent molecule should it fluoresce? is it something to do with the fluorescent indicator? can someone explain in details if possible. thank you Solution They appear as dark dots because the analytes that absorb UV quench the fluorescence and appear as dark spots in the glowing green background. Aspirin is a fluorescent molecule but it does not ehibit adequate fluorescence . Yes , we can do something to do with the fluorescent indicator. Fluorescent indicators are added to the plate .This indicator absorbs and emits UV light, which appears green. The presence of a UV active compound on the plate prevents the UV light from reaching those parts of the plate. This results in a darker coloration on the plate. We will be using colored compounds that are visible to the naked eye, as well as those that are visible under UV light. .

1. in thin layer chromatography aspirin and caffeine were used as spot. under uv light they appear
as dark dots. why do they appear as dark dots? but aspirin is a fluorescent molecule should it
fluoresce? is it something to do with the fluorescent indicator? can someone explain in details if
possible. thank you
Solution
They appear as dark dots because the analytes that absorb UV quench the fluorescence and
appear as dark
spots in the glowing green background.
Aspirin is a fluorescent molecule but it does not ehibit adequate fluorescence .
Yes , we can do something to do with the fluorescent indicator. Fluorescent indicators are
added to the plate .This
indicator absorbs and emits UV light, which appears green. The presence of a UV active
compound on the plate
prevents the UV light from reaching those parts of the plate. This results in a darker coloration
on the plate. We will
be using colored compounds that are visible to the naked eye, as well as those that are visible
under UV light.