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Resource Book for Sixth-Form Practical Chemistry

Experiment 11

Separation and Identification of the Major Components of Common Over-the-Counter Painkilling Drugs

image: Common painkilling tablets A quick-fit drying tube packed with anhydrous calcium chloride
image: Painkilling tablets ground into fine powder Painkilling tablets ground into fine powder
image: The tablet powder was suspended in dichloromethane Separation of acetaminophen/binder from aspirin/caffeine:

The tablet powder was suspended in dichloromethane and the suspension was warmed to about 30oC in a water-bath
image: the suspension was warmed to about 30oC in a water-bath
image: Filter the suspension Separation of acetaminophen/binder from aspirin/caffeine:

Filter the suspension

Solid residue:
acetaminophen and binder

Filtrate:
solution of aspirin and caffeine
image: The dichloromethane solution containing aspirin and caffeine The filtrate:

The dichloromethane solution containing aspirin and caffeine
image: Using the separatory funnel to separate aspirin and caffeine Separation of aspirin and caffeine by extraction:

The separatory funnel

Upper (aqueous) layer:
aspirin dissolved in 3M NaOH solution

Lower (organic) layer:
caffeine dissolved in dichloromethane
close-up image: the Upper (aqueous) layer - aspirin and Lower (organic) layer - caffeine
image: the aspirin and caffeine put into separate beakers Organic layer:
caffeine dissolved in dichloromethane

Aqueous layer:
aspirin dissolved in 3M NaOH solution
image: The aqueous solution containing aspirin was acidified with 3M HCl The aqueous solution containing aspirin was acidified with 3M HCl to about pH=2-3
image: Aspirin was precipitated out from the acidified solution Aspirin was precipitated out from the acidified solution
image: Isolating the aspirin Isolating the aspirin by suction filtration
image: The aspirin isolated from the painkilling tablet The aspirin isolated from the painkilling tablet
image: the standard samples Preparing standard sample solution for TLC analysis:

Dissolving the standard samples in methanol
image: Dissolving the standard samples in methanol
image: Marking the starting points on the TLC plate with a pencil Marking the starting points on the TLC plate with a pencil
image: Spotting the sample solutions onto the TLC plate with a capillary tube Spotting the sample solutions onto the TLC plate with a capillary tube
image: The TLC chamber and the eluting solvent for developing the TLC The TLC chamber and the eluting solvent for developing the TLC
image: Putting the TLC plate into the chamber with a pair of forceps Putting the TLC plate into the chamber carefully with a pair of forceps
image: Developing the TLC plate in the TLC chamber Developing the TLC plate in the TLC chamber
image2: Developing the TLC plate in the TLC chamber
image: The iodine chamber for visualizing the colorless sample spots on the TLC plate and text on image: Iodine crytals The iodine chamber for visualizing the colorless sample spots on the TLC plate
image: Spotting the sample solutions onto the TLC plate with a capillary tube The spots of aspirin and acetaminophen display as yellow-brown spots on the TLC plate inside the iodine chamber

left: aspirin
middle: caffeine
right: acetaminophen
image: The sample spots visualized on the TLC plate under ultraviolet radiation The sample spots visualized on the TLC plate under ultraviolet radiation

left: aspirin
middle: caffeine
right: acetaminophen

2004 Department of Chemistry, The Chinese University of Hong Kong