C-14 Carbon-14 Labeling & Synthesis Techniques 3

Question 1

What is the 'biosynthetic' approach to C-14 labeling?

Accepted Answer

Culturing organisms such as bacteria, algae, or plants in a 14CO2 atmosphere so they metabolically incorporate C-14

Answer

Chemical synthesis using only naturally derived biological reagents

Answer

Adding the C-14 label to a compound after biological extraction and purification

Answer

Enzymatic exchange of C-12 for C-14 in purified compounds in vitro

Question 2

Why must C-14 labeled compound synthesis be performed in a specialized radiochemistry laboratory?

Accepted Answer

To contain volatile C-14 gases (14CO2, H14CN), prevent personnel exposure, and properly manage radioactive waste streams

Answer

Standard organic reactions cannot proceed in the presence of radioactive atoms

Answer

Because all C-14 reactions require temperatures below -78°C

Answer

To prevent contamination of C-14 precursors with atmospheric stable C-12

Question 3

What minimum radioactive dose recovery is typically required to achieve acceptable mass balance in a human C-14 ADME study?

Accepted Answer

90% or greater recovery

Answer

At least 50% recovery

Answer

At least 75% recovery

Answer

Exactly 100% recovery

Question 4

What is the primary synthetic utility of C-14 labeled potassium cyanide (K14CN) in radiochemistry?

Accepted Answer

To introduce a C-14 labeled one-carbon unit as a cyano group, which can be converted to carboxylic acids, amines, or other functional groups

Answer

As an inert solvent for carrying out C-14 reactions

Answer

As a radioprotective scavenger to reduce radiolysis during synthesis

Answer

To measure reaction completion by monitoring radioactivity release

Question 5

What is the primary safety hazard when using 14C-labeled barium carbonate (Ba14CO3) as a C-14 source in synthesis?

Accepted Answer

Acid treatment liberates 14CO2 gas, which must be captured to prevent inhalation exposure and environmental contamination

Answer

It is highly flammable and poses a fire risk

Answer

It is shock-sensitive and prone to detonation

Answer

It reacts explosively with water at room temperature

Question 6

What distinguishes a 'carrier-free' C-14 compound from a 'no carrier added' (NCA) compound?

Accepted Answer

Carrier-free theoretically contains only C-14 labeled molecules with no stable C-12 isotopologues; NCA means no stable isotope was deliberately added but trace C-12 contamination may still be present

Answer

Carrier-free compounds always have higher radiochemical purity than NCA compounds

Answer

NCA compounds always achieve higher specific activity than carrier-free compounds

Answer

Carrier-free compounds can only be produced by biosynthetic methods

Question 7

What is the typical administered radioactivity range used in human C-14 ADME clinical studies?

Accepted Answer

100 to 250 μCi (3.7 to 9.25 MBq)

Answer

1 to 5 mCi (37 to 185 MBq)

Answer

1 GBq (27 mCi) or greater

Answer

No more than 3.7 kBq (100 nCi)