chlorophyll chromatography RP

describe how to separate photosynthetic pigments by chromatography (4)

• draw a line in pencil (origin line)

• fill test tube with solvent, ensuring it is below the origin line

• using a pipette/dropper, drop a few drops of chlorophyll solution onto origin line

• remove the paper from the test tube before the solvent reaches the end of the paper

how do you calculate the Rf value?

R_f value = distance travelled by pigment ÷ distance travelled by the solvent

what determines the distance travelled by a spot in TLC? (1)

the affinity for the stationary phase / balance between solubility in mobile phase and retention by stationary phase

why must the origin line be drawn in pencil not pen?

the ink and the leaf pigments would mix

why should you draw a line where the solvent reaches immediately?

the solvent evaporates rapidly, so the end position isn’t visible shortly after the experiment

why should you measure the Rf value from the middle of the pigment mark?

• the pigment mark is spread out

• by measuring from the middle position each time it’s a way to standardise the measurements you’re taking

• to allow comparisons

why should you make sure your chromatography paper is vertical and straight?

so the pigments move straight up the paper to avoid them running off the side and/or being washed off