Gas chromatography (GC) — unsuitable carrier gas choice In analytical gas chromatography, which gas is generally unsuitable as a carrier gas due to reactivity and the risk of oxidizing columns or analytes?

Introduction / Context:
The carrier gas in GC transports analyte vapors through the column and should be chemically inert and compatible with detectors. Common choices include helium, nitrogen, and hydrogen. Selecting an unsuitable gas can damage columns, distort chromatograms, and pose safety concerns.

Given Data / Assumptions:

• Capillary columns often contain stationary phases vulnerable to oxidation.
• Detectors (e.g., FID, TCD) require specific gas conditions for optimal performance.
• Safety and chemical inertness are primary criteria for carrier gas selection.

Concept / Approach:

Oxygen is reactive; it can oxidize stationary phases and sensitive analytes, shorten column life, and complicate detector operation. Therefore, oxygen is not used as a carrier gas. Helium and nitrogen are inert and widely used; hydrogen is also common due to efficiency benefits, though it requires careful handling because of flammability.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturer guidelines warn against oxygen contamination in carrier streams; oxygen is typically excluded using traps and leak-tested lines to prevent column degradation.

Why Other Options Are Wrong:

Nitrogen and helium are standard inert carriers. Hydrogen is suitable in many methods, improving efficiency and speed, though safety protocols are essential. “All of the above” is incorrect because not all listed gases are unsuitable.

Common Pitfalls:

Confusing detector fuel gases (e.g., H2 and air for FID flame) with carrier gases; or overlooking that trace oxygen contamination, even when using inert carriers, harms columns.

Final Answer:

Oxygen