Topic outline

  • Welcome to RADIOCHEMISTRY!

    Here you will learn about radioactive isotopes, how they are used in medicine and learn how to make them using column chromatography.

  • Print out Handnotes

  • Radioactive isotopes

    You should already know about isotopes, but what are radioactive isotopes?

    Watch the video below to find out more.



    • Medical radioisotopes

      Yttrium-90 (90Y) is an important radioisotope that is used to treat liver cancer. Tiny glass beads or microspheres filled with 90Y are placed inside the tumour’s blood supply, delivering a high dose of radiation to the cancer whilst blocking the blood supply – thereby killing it. This targeted delivery of radiation kills the cancerous cells while minimising exposure to healthy tissue. 

      90Y is formed when strontium-90 (90Sr) undergoes radioactive beta minus decay (β-):


      The short half-life (t½) of 90Y means that it can be implanted in the cancer and deliver a high dose of radiation in a relatively short time period. 90Sr would require a lot more material to deliver a similar radiation dose. Additionally Sr and Y behave differently in the body when washed out of the glass beads. Y is filtered by the kidneys and passed out as urine through the bladder. However, the body can mistake Sr  for calcium (Ca) so it can accumulate in bones. This is because Ca and Sr are both small dipositive cations (2+) whereas Y is larger and tripositive (+3).


      In your next chemistry class you will carry out an experiment to separate 90Sr and 90Y using column chromatography. In the next few pages you will learn the theory behind this experiment to help you in class.


      • Chromatography

        Chromatography provides an important method of separating, purifying and identifying components in a mixture.


        Types of chromatography include:

        • Thin-Layer Chromatography (TLC)
        • Column Chromatography (CC)
        • Gas Chromatography (GC)


        All forms of chromatography work on a similar principle. They all have a stationary phase (a solid, or a liquid supported on a solid) and a mobile phase (a liquid or a gas). The mobile phase flows through the stationary phase and carries the components of the mixture with it.  Each substance travels at a different rate depending on its solubility in the mobile phase and its retention (retardation) by the stationary phase.


        • Column Chromatography



          In column chromatography, a glass column is packed with an absorbent material (e.g. silica, ion exchange resin). This is the stationary phase.

          A solvent (water, acid or an oil) is then added to cover the stationary phase and ‘wet’ the entire column – this is how you set up the experiment.

          The mixture to be separated (e.g. radioactive solution) is then carefully added to the top of the column.

          The solvent is then allowed to run through the column, slowly and continually. The solvent is the mobile phase. It is important that the column never becomes ‘dry’ otherwise it can affect the separation.





          As the mobile phase runs though the column, the components of the mixture separate out as they move at different rates. This rate depends on how soluble each component is in the mobile phase and how strongly it is adsorbed onto the stationary phase.

          Components that adsorb strongly to the stationary phase will take a long time to travel down the column. Components that are very soluble in the mobile phase will pass through the column quickly. So it is a trade-off between how much a component sticks to the surface versus how quickly it is washed through by the solvent.

          Time taken for each component to reach the end of the column is known as the Retention Time.

           

          Watch the video below for more information on column chromatography!


          • The Experiment - Sr-90 / Y-90 Separation

            In your next chemistry lesson, you will separate two radioisotopes (90Sr and 90Y) using a form of column chromatography. Radioactive materials can be dangerous when handled improperly so you will use a robot to remotely handle the radioactive material. The experiment is actually set up in a laboratory in Germany!

            You will inject a radioactive solution of 90Sr and 90Y onto a separation column. The column is loaded with a crown-ether based ion exchange resin. At high nitric acid (HNO3) concentrations (>2 M ) strontium adsorbs strongly onto the resin. However, at low concentrations (<0.01 M) it will readily pass through the column. This is due to the resin’s capacity factor (k’):

             Sr resin capacity factor graph

            The capacity factor (retention factor) describes the migration rate of an analyte on a column. k’ is a measure of the time the analyte component (90Y or 90Sr) resides in the stationary phase relative to the time it resides in the mobile phase. If the analyte resides mainly in the stationary phase, then k’ is large. If the analyte resides in the mobile phase and moves quickly through the ion exchange resin, k’ is small.

            From the graph above, you can see that at high nitric acid concentrations, k' is large for Sr2+; indicating that strontium has adsorbed onto the stationary phase. At low concentrations Sr moves into the mobile phase and can exit the column (k' is small).


            • Ionlab - experimental apparatus

              In your next chemistry lesson you will be carrying out a column chromatography experiment, called "Ionlab".

              Examine the experimental set-up below. Once you have familiarised yourself, use your understanding of the theory to complete the experimental procedure.

              Apparatus

              • Solution containing 90Sr and 90Y
              • Syringe (to inject the solution)
              • Three valves to control the solvent (V1, V2, V3)  
              • Peristaltic pump
              • Solvent bottles (3 M and 0.0001 M HNO3)
              • Separation Column (ion exchange resin)
              • Geiger Counter (measures ionising radiation)
              • Waste container


              Look at the picture of the user interface below, this is how you will control the robot.





              • Ionlab - experimental procedure

                Use your understanding of column chromatography to complete the experimental procedure test below, or fill in the blanks in your hand notes.


                Prepare the column

                1. Open valve 3 (V3) in order to start the experiment.

                2. Set the solvent flow rate to ________.

                3. Select _________ solvent.

                4. Click on “start solvent pump” to begin pumping the solvent onto the column. Use the camera feed to check that the pump is rotating and droplets of solvent are landing on the slide.

                5. Allow the solvent to run for 5 minutes to ________ the entire column.

                6. Whilst waiting, set up your measurement parameters by going to the measurement tab. Set the measurement time to 3600 seconds (the duration of your experiment, 1 hour) and the counting interval to 10 seconds (this is how often the Geiger counter will record the activity).

                7. Click on “start measurement”.

                8. Make a note of the _________.


                 Separation of 90Y from 90Sr
                    
                 9.    After 5 minutes, stop the solvent pump.

                      10.  Click on ‘inject activity!’ The syringe will administer the 90Sr/90Y solution onto the top of the column.

                      11.  Start the solvent pump. Use the video to check that the solvent is flowing and that the measurement table is being filled.

                      12.  Allow the first peak in the chromatogram to build up and dissipate back to the background count rate.

                      13.  Select __________ solvent.

                      14.  Allow the second peak to build up and dissipate.

                      15.  The experiment is now complete. Email the data and log book to your school email address.

                      16.  Click on ‘logout and exit’.


                Missing words/phrases:

                3 M HNO3

                background count rate

                1ml/minute

                0.0001 M HNO3

                'wet' the entire column

                'inject activity!'