Gas Chromatography—What Is Column Bleed? In capillary GC, the term “column bleeding” refers to which phenomenon under typical operating conditions (especially at elevated oven temperatures)?

Introduction / Context:
“Column bleed” is a common term in gas chromatography describing a baseline rise or noise as the oven temperature increases. Understanding the source of bleed helps diagnose baseline issues and decide when a column has aged or is being over-stressed by method conditions.

Given Data / Assumptions:

• Capillary GC column using a polymeric stationary phase (e.g., polysiloxane).
• Method includes temperature programming to high oven temperatures.
• No catastrophic mechanical damage is indicated.

Concept / Approach:
At elevated temperatures, very small amounts of the stationary phase can thermally degrade or volatilize, slowly eluting and causing a baseline elevation or drift at the detector. This is termed “column bleed.” It is distinct from mechanical leakage or analyte tailing.

Step-by-Step Solution:

Verification / Alternative check:
Bleed often scales with temperature and column age; switching to a low-bleed phase or lowering maximum temperature reduces the effect.

Why Other Options Are Wrong:

• Extended analyte elution describes retention, not bleed.
• Cracked columns or injuries are mechanical issues, not the definition of bleed.
• Septum debris relates to inlet contamination, not stationary-phase elution.

Common Pitfalls:
Misattributing elevated baselines to contamination rather than inherent high-temperature bleed. Always check method maximum temperature versus column limits.

Final Answer:
Elution of traces of the stationary phase from the column