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Lesson 14

Lesson 14. Radiotracers. Introduction. Basic principle: All isotopes of a given element will behave identically in most physical, environmental and biological environments. Ea sier to detect radioactive atoms than stable atoms. Simple Cheap

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Lesson 14

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  1. Lesson 14 Radiotracers

  2. Introduction • Basic principle: All isotopes of a given element will behave identically in most physical, environmental and biological environments. • Easier to detect radioactive atoms than stable atoms. • Simple • Cheap • Amazing breadth of applications. Now part of the standard arsenal of analytical techniques

  3. Designing a Radiotracer Experiment • Radioactive isotopes of a given element behave the same as stable isotopes. • Isotope Effect--Most concern for H, 15% effect for 12C vs 14C. • Nonisotopic tracers

  4. Intermolecular vs Intramolecular Effects • Intramolecular--decarboxylation of malonic acid (HOO14C-12CH2-12COOH) • Intermolecular--decarboxylation of benzoic acid-7-14C (C6H5-14COOH vs C6H5-12COOH)

  5. Basic Principle #2 • Radioactivity does not change the chemical and physical properties of the system. • Tracer activities, bond strengths, energy of emitted radiation • 3H problem • “Daughter atom problems”

  6. Basic Principle #3 • No deviation from normal physiological state. • Injecting stable as well as radioactive material

  7. Basic Principle #4 • Chemical and physical form of the labeled material is the same as the un-labeled material. • Aqueous chemistry • Adsorption, carriers, carrier-tracer exchange • Radiochemical purity • Position of the label

  8. Basic Principle #5 • Label stays intact

  9. Practical Considerations • Availability of tracer • t1/2 • Labeling, position of the label • Ease of detection • Health and safety aspects • Waste disposal

  10. Calculation of the amount of tracer needed • No excuse for turning a tracer experiment into a detection problem. • Statistics (> 104 cts) • Counting efficiency, detector type, geometry factors, chemical yields • Safety factor

  11. Hazard evaluation • Dose rates, RBEs • Effects on physiology • Waste problems • Green chemistry

  12. Radiotracer Preparation Commonly Used Tracers 3H(T) R 12.33 yr - 0.018 14C R 5730 yr - 0.156 22Na C 2.60 yr +,  1.274 24Na R 15.0 hr  1.369 32P R 14.3 d - 1.71 • n-rich vs p-rich • PET nuclides

  13. Labeling • Position: acetic-1-14C acid = CH314COOH, acetic-2-14C acid = 14CH3COOH • Terms; Specifically labeled, U, N G

  14. Methods of labeling • Chemical synthesis,best except for chirality • Biological synthesis, tedious • Tritium • Commercial supplier problems

  15. Physical tracers • Wear, corrosion • Mixing • Fluid motion • Pollutant tracing • Measuring unknown volume

  16. Chemical Applications • Test separation procedures • Ksp measurements • Exchange reactions • Chemical reaction mechanisms

  17. Example • Cyclization of -phenoxyacetophenone to 2-phenylbenzofuran

  18. Physical Isotope Effects • Gaseous diffusion • Distillation

  19. Chemical Isotope Effects

  20. Kinetic Isotope Effects

  21. Biological applications Autoradiography

  22. DNA Analysis

  23. Radioimmunoassay

  24. Figure 19. The radioimmunoassay technique to measure hormone levels in the body involves mixing natural hormones (from a blood sample) and radioactively prepared hormones together, and adding that mixture to a solution containing artificially produced antibodies. The two hormones compete for binding sites on the antibodies. The hormones attach to the antibodies in amounts that ore proportional to their concentration.

  25. Environmental Applications of Radiotracers • Used in tracing pollutant motion in atmosphere, hydrosphere, lithosphere Advantages of radiotracers • Not influenced by state of system • Highly penetrating • Good detection sensitivity • If t1/2 short, will disappear after expt. • Cheap BIG PROBLEM--HP

  26. Typical Environmental Radiotracers • 41Ar • 24Na • 82Br • 140La

  27. Industrial Uses of Radiotracers

  28. Nuclear Medicine • Therapy and diagnosis • Most important radionuclides are 99Tcm and the I isotopes. Over 90% of procedures involve these nuclei

  29. 99Tcm • 143 keV gamma rays • 6 hr t1/2 • Use of generators

  30. PET, Positron Emission Tomography

  31. Isotope Dilution Analysis • Direct IDA • In direct IDA, we are faced with the problem of determining the amount of some inactive material A in a system. Let us define this unknown amount as x grams. To the system containing x grams of inactive A, we add y grams of active material A* of known activity D. Thus we know the specific activity of the added active material, S1.

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