Cap Liner

• A liner is typically installed in a solid-top cap (i.e., a cap without a hole).
• It cannot be pierced and is not designed for needle access.
• Its primary function is to seal the vial, preventing sample evaporation or contamination during storage or transport.
• Liners may be made from materials such as PTFE, silicone, or polyethylene, and are selected based on chemical compatibility.

Cap Septum

• A septum (plural: septa) is installed in an open-top cap, which has a hole to allow needle access.
• It is designed to be pierced by an autosampler needle or syringe during sample injection.
• After piercing, the septum reseals itself, maintaining vial integrity and minimizing exposure to air or contaminants.
• Septa are often made from layered materials (e.g., PTFE/silicone) to balance chemical resistance and resealability.

🔍 Fun Fact: The term septum comes from Latin, meaning “a wall” or “partition.” In chromatography, it acts as a barrier that protects the sample until it's accessed.

Why It Matters

• Using the correct closure type is essential for sample integrity, instrument compatibility, and analytical accuracy.
• Always match the cap type (solid or open-top) with the appropriate liner or septum based on your application—whether for storage or injection.