C-14 Carbon-14 Labeling & Synthesis Techniques 1 — Questions and Answers
Question 1: What is the established half-life of Carbon-14?
- 5,268 years
- 1,600 years
- 12.3 years
- 5,730 years (Correct answer)
Correct answer: 5,730 years
Carbon-14 has a half-life of approximately 5,730 years, which makes it valuable for radiocarbon dating and long-duration metabolic tracing studies.
Question 2: What type of radiation does Carbon-14 emit during its decay?
- Alpha particles
- Low-energy beta particles (Correct answer)
- Gamma rays
- Positrons
Correct answer: Low-energy beta particles
C-14 is a pure beta emitter with a maximum energy of 156.5 keV, classifying it as a low-energy beta emitter that requires liquid scintillation counting for detection.
Question 3: What does 'specific activity' mean for a C-14 labeled compound?
- The chemical purity percentage of the compound
- The amount of radioactivity per unit mass or mole (e.g., Ci/mmol or GBq/mmol) (Correct answer)
- The rate of radiolytic decomposition over time
- The percentage of label located at a single molecular position
Correct answer: The amount of radioactivity per unit mass or mole (e.g., Ci/mmol or GBq/mmol)
Specific activity expresses how much radioactivity is present per unit quantity of compound, indicating what fraction of the molecules carry the C-14 label.
Question 4: In C-14 synthesis, what does 'position-specific labeling' mean?
- Incorporating C-14 at every carbon position in a molecule
- Placing C-14 at one defined, predetermined carbon position within the molecular structure (Correct answer)
- Using multiple radioisotopes simultaneously in the same molecule
- Labeling only the terminal carbons of an aliphatic chain
Correct answer: Placing C-14 at one defined, predetermined carbon position within the molecular structure
Position-specific labeling places C-14 at an exact, known carbon atom, enabling researchers to track the metabolic fate of that specific bond or functional group.
Question 5: Which primary approach is used to introduce C-14 into organic molecules at specific positions during synthesis?
- Neutron bombardment of the finished compound
- Building the molecule from C-14 labeled small-molecule precursors such as 14CO2, K14CN, or 14CH2O (Correct answer)
- Isotope exchange reactions triggered by ultraviolet light
- Electrochemical reduction using C-14 coated electrodes
Correct answer: Building the molecule from C-14 labeled small-molecule precursors such as 14CO2, K14CN, or 14CH2O
C-14 labeled compounds are synthesized by incorporating C-14 labeled building blocks (such as 14CO2, K14CN, or 14CH2O) at a defined step in a classical organic synthesis sequence.
Question 6: What is the maximum beta particle energy (Emax) emitted by Carbon-14?
- 18.6 keV
- 156.5 keV (Correct answer)
- 546 keV
- 1.71 MeV
Correct answer: 156.5 keV
C-14 emits beta particles with a maximum energy of 156.5 keV, making it a low-energy beta emitter compared to high-energy emitters like P-32 (1.71 MeV).
Question 7: Why is C-14 often preferred over stable C-13 for metabolic tracing in pharmaceutical research?
- C-14 is always less expensive to produce than C-13 enriched compounds
- C-14 can be detected at trace concentrations using radioactivity counting, without requiring mass spectrometry (Correct answer)
- C-14 participates in a greater variety of chemical reactions than C-13
- C-14 is metabolized more slowly, allowing longer study windows
Correct answer: C-14 can be detected at trace concentrations using radioactivity counting, without requiring mass spectrometry
Radioactivity-based detection (liquid scintillation counting, AMS) is extremely sensitive, enabling C-14 tracing at very low concentrations without the need for expensive, specialized mass spectrometry instrumentation.
C-14 Carbon-14 Labeling & Synthesis Techniques 1
What is the established half-life of Carbon-14?