C-14 Carbon-14 Labeling & Synthesis Techniques 2

Question 1

What is 'radiochemical purity' (RCP) for a C-14 labeled compound?

Accepted Answer

The fraction of total radioactivity present as the desired labeled chemical species

Answer

The absence of any non-radioactive chemical impurities

Answer

The ratio of C-14 atoms to C-12 atoms in the compound

Answer

The compound's stability percentage over its labeled shelf life

Question 2

Which analytical method is most commonly used to assess the radiochemical purity of C-14 labeled compounds?

Accepted Answer

Radio-HPLC or radio-TLC with in-line radioactivity detection

Answer

Infrared spectroscopy (IR)

Answer

Electrospray mass spectrometry (ESI-MS)

Answer

UV-Vis spectrophotometry

Question 3

What is 'radiolytic decomposition' in C-14 labeled compounds?

Accepted Answer

Self-induced radiation damage that breaks the labeled molecule's chemical bonds over time

Answer

Intentional thermal degradation of labeled compounds for waste disposal

Answer

The natural nuclear decay of C-14 to nitrogen-14

Answer

Chemical decomposition caused by exposure to ambient light

Question 4

Which storage practice best minimizes radiolytic decomposition of C-14 labeled compounds?

Accepted Answer

Dilute to low radioactive concentration, store frozen, and add a radical scavenger such as 1-5% ethanol

Answer

Store at room temperature in dark amber vials with no additives

Answer

Purge storage vials with oxygen to prevent oxidative radiolysis

Answer

Store at high concentration so fewer solvent molecules absorb the radiation

Question 5

In a C-14 ADME study, what does total radioactivity measured in plasma represent?

Accepted Answer

The combined signal from the parent compound plus all metabolites that retain the C-14 label

Answer

Only the unchanged parent drug concentration

Answer

The rate of radioactive decay in the blood compartment

Answer

The fraction of dose absorbed from the gastrointestinal tract

Question 6

What is the primary shelf-life concern for high-specific-activity C-14 labeled compounds?

Accepted Answer

Progressive radiolytic decomposition reducing radiochemical purity below an acceptable threshold (typically 95% RCP)

Answer

Chemical hydrolysis unrelated to radioactivity

Answer

Isotopic exchange of C-14 with environmental C-12 carbon dioxide

Answer

Nuclear transmutation reactions at ambient temperature

Question 7

For which application is a uniformly labeled C-14 compound, designated [U-14C], most appropriate?

Accepted Answer

Measuring overall radioactive recovery and mass balance in ADME studies

Answer

Studying the metabolic fate of a single specific functional group

Answer

Determining which specific bond is cleaved during an enzyme-catalyzed reaction

Answer

Tracking only the carboxyl group carbon through metabolic pathways