2 Required practical 12: Thin-layer chromatography

A-level Chemistry exemplar for required practical No. 12 Separation of species by thin-layer chromatography: Analysis of the composition of some common medicines Student sheet Requirements You are provided with the following:  ethanol or other solvent  ethyl acetate  ibuprofen tablet  paracetamol tablet  caffeine tablet  aspirin tablet  Anadin Extra tablet (or equivalent containing aspirin, paracetamol and caffeine)  pestle and mortar  weighing boat or bottle  TLC plate  capillary tubes  developing chamber (or suitable container with lid)  access to UV lamp. Suggested method Preparation of samples a) Use a pestle and mortar to crush the aspirin tablet and transfer to a weighing boat or bottle. b) Dissolve approximately 0.1 g of the powdered tablet in 0.5 cm3 of ethanol. c) Repeat steps (a) and (b) with the ibuprofen tablet and the paracetamol tablet. d) Use a pestle and mortar to crush the caffeine tablet and transfer to a weighing boat or bottle. e) Dissolve approximately 0.1 g of the powdered tablet in 7.0 cm3 of ethanol. f) Repeat steps (d) and (e) with the Anadin Extra tablet. Thin-layer chromatography a) Carefully use a pencil to draw a faint line 1 cm above the bottom of a TLC plate and mark five spots, equally spaced along this line. b) Use a capillary tube to apply a tiny drop of each solution to a different origin spot and allow the plate to air dry. c) Add approximately 10 cm3 of ethyl acetate to a development chamber (or suitable container with a lid) d) Place the TLC plate into the developing chamber, making sure that the level of the solvent is below the spotting line. Replace the lid and make sure it is a tight seal. e) When the level of the solvent reaches about 1 cm from the top of the plate, remove the plate and mark the solvent front with a pencil. Allow the plate to dry in the fume cupboard. f) Place the plate under a UV lamp in order to visualise the spots. Draw around them lightly in pencil. g) Calculate the Rf values of the observed spots.