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

Radiochemical purity (RCP) is the percentage of total radioactivity that exists as the specified chemical form of the labeled compound, distinguishing it from radioactive degradation products.

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

Radio-HPLC and radio-TLC separate chemical species chromatographically while simultaneously detecting radioactivity, enabling identification and quantification of all C-14 containing species.

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

Radiolytic decomposition occurs when beta radiation emitted by C-14 (or by surrounding solvent molecules) generates reactive radicals that damage the chemical bonds of the labeled compound.

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

Low radioactive concentration reduces the dose rate per unit volume, freezing slows chemical reactions, and radical scavengers like ethanol quench reactive intermediates generated by radiolysis.

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

Total plasma radioactivity reflects the C-14 signal from both the parent compound and all radioactive metabolites, providing an integrated view of drug-related material in the systemic circulation.

C-14 - C-14 Radioisotope Certification Practice Test

C-14 - C-14 Radioisotope Certification Practice Test

C-14 Carbon-14 Labeling & Synthesis Techniques 2