required practical 12

separation of a species by thin-layer chromotography (TLC)

• crush any solid tablets with a pestle and mortar • weigh out approximately 0.1g of each powdered tablet and then dissolve in 0.5cm3 of ethanol • whilst wearing gloves, use a pencil to draw a line 1cm above the bottom of a TLC plate and mark however many spots there are samples equally spaced over the line • use a capillary tube to add a tiny drop of each sample to a different spot, then let the TLC plate air dry • add a solvent to a development chamber or beaker wih a lid - it shouldn’t be more than 1cm in depth • place the TLC plate in the chamber/beaker, ensuring the level of the solvent is below the pencil line, and replace the lid to get a tight seal • when the level of the solvent reaches about 1cm from the top of the plate, remove the plate and use a pencil to mark the solvent front • place the plate in a fume cupboard to dry • place the plate under a UV lamp to see the spots, and draw lightly around them in pencil • calculate the Rf values of the spots

distance travelled by compound/distance travelled by solvent

to prevent contamination from your hands to the plate

it won’t dissolve in the solvent

if the drop is too big, it will cause different spots to merge

if it is too deep it will dissolve the sample spots from the plate (solvent depth must be below starting line)

• to prevent the toxic solvent from evaporating from the beaker and plate • to ensure the atmosphere in the beaker is saturated with solvent vapour

to get more accurate results (but Rf value can still be calculated if solvent front doesn’t reach top)

because the solvent is toxic