the extraction & purification of paracetamol from tablets

method

1. warm 2 paracetamol tablets with propane (20cm3) in a small conical flask by placing the flask in warm water.

2. once the tablets have broken up, the undissolved material (binding agents and filler) should be removed using filter paper & funnel. Allow propane to evaporate, either overnight or on a warm bath in a fume cupboard.

3. the white solid is crude paracetamol. Keep a small amount of the solid to dtermine its melting point later. The material can be purified by recrystallisation from water.

4. heat the solid in about 10cm3 of water to dissolve it, & filter off any insoluble material through a very small piece of cotton wool in a warm glass funnel. (pour hot water through the funnel & cotton wool first).

5. cool the filtrate, and filter off the crystals that form.

6. dry the pure paracetamol by either pressing with filter papers or gently warming in an oven.

Question:

How would you modify this procedure in order to determine which brand of paracetamol tablets contains the greatest quantity of active ingredient?

I don't think I'd modify the procedure at all. You wouldn't necessarily need to recrystallize the pro
Duct (steps 4-6) if it's reasonably pure, which it should be.

That's not to say that there aren't better ways to analyze the substance. There are. But if you wish to use this procedure to analyze it, then I'd probably do steps 1 and 2 and forget the rest.

However if you had to modify it what would you do because I need to give a reason

The biggest problem is that you lose material when you recrystallize it. You get a very pure product, but that is not important if you wish to analyze the sample. If you do steps 1 and 2, you are eliminating any insoluble material (insoluble fillers, etc), and are quantitatively keeping the desired material in one phase. That's the good point. In step 4, you again filter off any insoluble material. That's another good thing because insoluble material is not paracetamol, so you're getting rid or some of the impurities. The big problem with the method is that you filter off the crystals that form and ignore any material that might still be in solution.

So... (thinking)... How would I modify it? I would probably do some experimentation and try to find a recrystallization solvent that worked better than water. I would also try to get a recrystallization solvent that could be cooled more than you can with water (below 0 Celsius) so that, hopefully, I could get quantitative deposition of the desired product.

Sorry. That's all I can think of. I've never analyzed this material.