Quantifying retention in chromatography — Which of the following metrics are used to measure how long a sample is retained on a column?

Introduction / Context:
Chromatographic performance and identification rely on standardized ways to describe retention. Several complementary metrics exist: raw times, normalized factors, and indices for cross-lab comparability (especially in gas chromatography).

Given Data / Assumptions:

• t_R measures when a solute elutes.
• k' normalizes retention to the dead time (k' = (t_R − t_M) / t_M).
• Retention index (e.g., Kovats index) aligns unknowns to reference homologous series (GC).

Concept / Approach:
Each metric captures retention from a different angle. t_R is instrument-specific; k' enables method comparison; retention index supports identification across systems. Taken together they characterize retention robustly.

Step-by-Step Solution:

Verification / Alternative check:
Switching flow rate changes t_R but leaves k' more stable; index remains comparable when calculated versus reference standards.

Why Other Options Are Wrong:

Common Pitfalls:
Using raw t_R to compare across different instruments without normalization; use k' or indices instead.

Final Answer:
All of these.