Learning Goals

To prepare a sample of radiolabelled aspirin and measure the yield of the reaction radiometrically

Explanation and Exercise Guide

Theory

The study of chemical metabolism in the body is greatly facilitated by the availability of compounds labelled with a radioactive atom. Such an example is 14C-labelled aspirin. This experiment will show you how to prepare this compound labelled in the acetyl group, and will illustrate some of the special techniques used in synthesising radioactive compounds.

Experimental Procedure

experimental procedure for radiolabelling of aspirin

Questions for the Students

• Calculate the chemical yields for both crops of aspirin and determine their activities from the above counting results.
  • Specific activity of first crop of aspirin S1 = -------------- dpm mg-1.
  • Specific activity of scavenged aspirin S2 = ---------------- dpm mg-1.
• As has already been stated, the aspirin is partially soluble in the original filtrate, and it is possible to determine how much labelled aspirin is present in this filtrate and hence determine the total amount of aspirin produced by the acetylation and not solely the amount extracted.
• Let the amount of aspirin in the filtrate be x mg. It will have the same specific activity as the first crop of aspirin, S1 dpm mg-1.
• After addition of 150 mg of inactive aspirin, the new specific activity was S2 dpm mg-1.
• Now total activity = S1 x and this must equal S2 (+ 150) after dilution.
• Therefore, S1 x = S2 (x + 150).
• The values of S1 and S2 have already been determined and hence x can be calculated.
• The value of x should be added to the total weight of the original crop of aspirin to give the total yield of aspirin from the acetylation reaction.

1. Why was the yield not 100%?
2. Why was inactive aspirin was added as a scavenger?

Other

How to do calculations or other important aspects for the theory that is not directly related to exercise.

Safety Aspects

• Wear a lab coat, disposable gloves and safety glasses
• DO NOT dispose of any liquid or solid waste down sinks or in waste bins. Place in the red waste buckets provided.
• Care must be taken when using toluene. Avoid inhaling fumes as it may cause dizziness or nausea. It is also highly flammable.

Equipment

Description of the equipment needed and used during the exercises.

Preparation for the lab Supervisor

The preparation that the lab Supervisor needs to do to ready the lab.

Feedback from Users and Supervisors

Here there should be a link to a open page where people who have used the exercise can leave feedback. How the exercises worked and troubles in performing it.

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