32. The process of release of volatile / soluble components of a GC or HPLC stationary phase is termed as:
A. Bleed
B. Creep
C. Back flush
D. Back diffusion
Stationary phase bleed is the correct term for the release of volatile/soluble components from GC or HPLC columns, making option (A) Bleed correct. This phenomenon affects baseline stability and detector performance.
Option Analysis
Bleed (A): Refers to the gradual release of stationary phase polymer fragments (siloxanes in GC) due to thermal degradation at high temperatures. Appears as rising baseline noise, especially in MS detectors.
Creep (B): Not a chromatography term. In materials science, describes slow deformation under stress, irrelevant to column stationary phases.
Back flush (C): Technique where carrier flow reverses direction to elute heavy compounds quickly or clean columns. Purposeful operation, not passive component release.
Back diffusion (D): Describes analyte molecules diffusing against mobile phase flow, contributing to band broadening (A-term in van Deemter). Not stationary phase degradation.
Stationary phase bleed in chromatography occurs when volatile components from GC/HPLC columns elute, creating baseline drift and ghost peaks. Critical for trace analysis and maintaining instrument sensitivity.
Bleed Characteristics & Causes
-
GC Columns: Polysiloxane degradation releases siloxanes (m/z 207, 281, 355 in MS)
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Temperature dependent: Increases exponentially above 250°C
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Thicker films bleed more due to greater polymer mass
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Oxygen catalyzes backbone cleavage via “back-biting” reaction
Troubleshooting Bleed
| Issue | Symptom | Solution |
|---|---|---|
| High bleed | Rising baseline >300°C | Condition column, use low-bleed phases |
| Ghost peaks | Regular intervals | Replace column, check septa |
| MS contamination | High m/z 207/281 | Bakeout, new column liner |
Prevention: Ultra-low bleed phases (HT-5, DB-5ms), proper conditioning (30 min at max temp), oxygen-free carrier gas.
Exam Context
GATE Life Sciences tests chromatography artifacts distinguishing operational techniques (backflush) from degradation phenomena (bleed). Baseline rise at high temperature = bleed signature question pattern.
Key takeaway: Bleed = stationary phase loss; affects ALL columns over time but minimized with proper maintenance.
