Thin Layer Chromatography

Question 1

method

Answer 1

a) Wearing gloves, draw apencilline1 cm above the bottom of a TLC plate and markspots for each sample, equally spaced alongline.
b) Use a capillary tube toaddatiny drop of each solution to a differentspotand allow the plate to air dry.
c) Add solvent to achamber or large beaker with a lid so that is no more than1cm in depth
d) Place the TLC plate into thechamber ( alt.Roll up paper and stand it in a large beaker) ,making sure that the level of the solvent is below thepencilline. Replace thelidto get a tight seal.
e) ( alt.allow to stand for twenty minuetes) When the level of the solvent reaches about 1 cm from the top of the plate, remove the plate and mark the solvent level with a pencil. Allow the plate toddy in the fume cupboard. (alt.Spray paper with ninhydrinand put in oven)
f) Place the plate under a UV lamp in order to seethe spots. Draw around them lightly in pencil.
g) Calculate the Rf values.

Question 2

why Wear plasticgloves

Answer 2

to prevent contamination from the hands to the plate

Question 3

why a pencilline –

Answer 3

will not dissolve in the solvent

Question 4

why tinydrop

Answer 4

–too big a drop will cause different spots to merge

Question 5

why a Depthof 1cm solvent

Answer 5

–if the solvent is too deep it will dissolve the sample spots from the plate

Question 6

why lid–

Answer 6

to prevent evaporation of toxic solvent

Question 7

Rf value can be calculated if the solvent front does not reach the top of the plate.

however?

Answer 7

Will get more accurate results if the solvent is allowed to rise to near the top of the plate

Question 8

why dry in a fume cupboard

Answer 8

the solvent is toxic

Question 9

what If the stops are colourless and not visible

Answer 9

UV lamp used

Question 10

why wont some substances separate

Answer 10

Some substances won’t separate because similar compounds have similar Rf values. So some spots may contain more than one compound