Capillary GC hardware — What is the typical internal diameter (ID) range for fused-silica capillary GC columns used for routine analytical separations?

Introduction / Context:
Choosing the internal diameter (ID) of a GC capillary column affects efficiency, capacity, head pressure, and optimal linear velocity. Analysts should know the common ID ranges used in routine work to make sensible method choices.

Given Data / Assumptions:

• Common analytical capillary IDs include approximately 0.10, 0.18, 0.25, 0.32, and 0.53 mm.
• 0.25 mm ID is a classic default; 0.32 mm is also widely used for robustness.
• Narrower IDs provide higher efficiency but lower capacity and higher pressure.

Concept / Approach:
For typical analytical separations (split/splitless injection) the most commonly used IDs cluster around 0.25 mm (within 0.2–0.3 mm). While 0.32 mm columns are also popular, the representative “typical” analytical range centers on 0.2–0.3 mm in many textbooks and vendor guides, with 0.25 mm being the workhorse choice.

Step-by-Step Solution:

Verification / Alternative check:
Column manufacturer catalogs highlight 0.25 mm ID as the default for general use; many validated methods specify 0.25 mm ID columns.

Why Other Options Are Wrong:

• 0.3–0.5 mm and above: wider-bore columns trade efficiency for capacity; less common as the default analytical choice.
• 0.5–2.0 mm: typically used for special applications or packed-column substitutes.
• 0.05–0.10 mm: micro-/narrow-bore requiring specialized systems and very high pressures.

Common Pitfalls:
Assuming wider ID always improves sensitivity; efficiency and split ratios often favor 0.25 mm for routine work.

Final Answer:
0.2–0.3 mm.