Medication delivered in the form of a pill contains an active ingredient or ingredients. Beside the drug itself, the pill also contains "fillers". The filler has several functions. It can mask an unpleasant taste or can be used to make up the bulk of the pill if the actual drug content is too small to be easily manageable. The filler can affect the rate of drug delivery, which is why many fillers are polysaccharides since they will allow the pill to fall apart in the stomach due to the action of stomach acids; this will speed up the delivery to the stomach or intestines.

Drugs that have the same generic name have the same active ingredient, the dosage of which must be listed. However, the amount and composition of the filler does not have to be listed.

In this experiment, you will measure the amount of active ingredient in aspirin pills (acetylsalicylic acid) and the amount of filler, based on their differing solubility in ethanol. The active ingredient is very soluble in ethanol, but the fillers used are generally not.

EXPERIMENTAL PROCEDURE

1. Take 8 aspirin tablets, weigh them and record their total weight. Look on the packet and record how much active ingredient there should be per tablet.

2. Take the tablets and grind them in a pestle and mortar. While you are doing this, stand the pestle and mortar on a sheet of paper in order to catch any bits that might spill out. Grind the tablets into a fine powder and tip any spillages back in.

3. Add 10ml of 95% ethanol to the mortar and continue to grind for about two minutes.

4. Weigh a piece of filter paper and record its weight. Place the filter paper in a funnel and put this into a conical flask. Transfer the liquid from the mortar into the funnel and use a glass rod to scrape out all the bits. After a few minutes, when you have at least 1ml of filtrate in the flask, lift the funnel and allow one drop to fall onto a microscope slide. Replace the funnel in the flask and put the slide to one side to allow the liquid to evaporate. Observe what happens to the drop on the slide.

5. Add another 10ml of ethanol to the mortar and tip it into the funnel and filter it into a fresh flask (using the same funnel and filter paper, which will have a white solid in it). Using a fresh (labelled) microscope slide, repeat the drop procedure and allow it to dry.

6. Repeat step 5 twice more. Record what you see on each of the four slides.

7. Measure and record the volumes of the filtrates in each flask and keep the filtrates safe for the direct determination of their aspirin content.

8. Transfer the filter paper to a 100ml beaker and put it in the drying oven for about 15 minutes, until the powder is dry.

9. Remove the HOT! beaker and allow it to cool. Weigh the now dry filter paper containing the powder and record the weight. Work out the weight of the filler.

10. Put a small amount of the dried filler onto a white tile and add a drop of the iodine solution. A blue/black colour will indicate the presence of starch. Was there any?