chromatography Flashcards
what is the purpose of chromtography
to separate compounds based on their partitioning between a mobile phase and a stationary phase
in a TLC, what is the stationary phase?
it is a SOLID POLAR phase made of silica gel or Alumina gel, molecules with POLARITY will FAVOR the stationary phase and have lower Rf values and stay further down
in TLC what is the mobile phase
it is the LIQUID, it is NONPOLAR so nonpolar molecules will travel UP the plate
what travels faster up a plate? nonpolar solids or polar solids
nonpolar solvents have an affinity for the nonpolar mobile phase and will travel up faster by capillary action
how does chromatography separate
by polarity
how does gas chromatography separate
by boiling point
why do we add blotting paper to the developing jar
to ensure that the atmosphere is saturated with the vapors of the developing solvent
if it is not saturated, it will evaporate off and the TLC will stop
why do the spots on the starting line need to be above the liquid
they will otherwise dissolve off
why can you not touch the TLC plate when it is traveling?
it will stop the TLC
how can you visualize a TLC
either with your eye, I2 stain, or if its conjugated you can visualize it under UV
if you have a polar compound, will it have a large or small Rf value
you will have a small Rf value, it will stick to the stationary phase and not move very far
if you have a nonpolar compound, will you have a large or small Rf value
large, it will prefer the mobile phase and travel further up
if a solvent is made less polar, what happens to the Rf
the Rf will decrease
if the solvent is increased in polarity, what happens to the Rf
the Rf will increase
what is the absorbant
it is a polar stationary phase
what is the eluant
it is the nonpolar mobile phase
functional groups that are more polar tend to elute
slower and have a smaller Rf value
if the mobile phase is too polar
everything moves to the top because the mobile and stationary are too similar
if mobile phase is too nonpolar
nothing moves, they are too dissimilar
to determine reaction progress, what are the four lanes in TLC
the first lane is the starting material, with the polar molecules near the bottom
the second lane is a ixed co-spot
the third and fourth are product fractions that show the various polarities of products
what is the two main differences with column chromatography and tlc
column allows larger scale separation and the mobile phase moves down with gravity rather than down
in column chromatography, what elutes first
compounds with higher Rf, nonpolar, will elute first as they favor mobile phase
in a column chromatography, what elutes later
the compounds with lower Rf, are polar, will elute later as they favor stationary
