Analytical derivatization — Why is chemical derivatization of analytes commonly performed before chromatographic analysis (especially GC)?
-
ATo reduce excessive polarity and hydrogen bonding that hinder elution
-
BTo increase detector response or selectivity for certain detectors
-
CTo increase volatility and thermal stability for GC analysis
-
DAll of the above
-
ETo eliminate the need for calibration standards
Answer
Correct Answer: All of the above
Explanation
Introduction / Context:Derivatization modifies analyte functional groups to improve chromatographic behavior and detection. It is a key strategy in gas chromatography and sometimes in LC when sensitivity or selectivity needs enhancement.
Given Data / Assumptions:
- Polar functional groups (e.g., −OH, −NH2, −COOH) cause strong adsorption and tailing.
- Many detectors respond better to certain chemical moieties.
- GC requires analytes to be sufficiently volatile and thermally stable.
Concept / Approach:Assess each benefit: silylation, acylation, or alkylation reduces polarity; electron-capturing tags enhance ECD response; fluorescent or UV tags boost LC detector sensitivity; volatility and stability often improve, enabling cleaner peaks and better quantitation.
Step-by-Step Solution:
Choose appropriate reagent (e.g., BSTFA for silylation).React functional groups to form less polar, more volatile derivatives.Match derivative to detector (e.g., nitro-derivatives for ECD).Verification / Alternative check:Compare chromatograms pre- and post-derivatization: reduced tailing, improved peak symmetry, and higher signal-to-noise validate the approach.
Why Other Options Are Wrong:
e) Calibration is still required; derivatization does not remove the need for standards.Common Pitfalls:Incomplete derivatization yields multiple peaks; always validate reaction completeness and stability.
Final Answer:All of the above.