Quantifying retention in chromatography — Which of the following metrics are used to measure how long a sample is retained on a column?
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ARetention time (t_R)
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BRetention factor (k')
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CRetention index (particularly in GC)
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DAll of these
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EPeak height alone
Answer
Correct Answer: All of these
Explanation
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:
List metrics applicable to retention → t_R, k', retention index.Note scope → k' (LC and GC); index widely used in GC.Conclude that all listed metrics are measures of retention.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:
e) Peak height reflects detector response and concentration, not retention directly.Common Pitfalls:Using raw t_R to compare across different instruments without normalization; use k' or indices instead.
Final Answer:All of these.