For HPLC Vial Caps and Septa, you need to know
Vial caps play a crucial role in guarding the sample from spills, contamination, and evaporation. Ideally, caps should form an airtight seal and be inert. Caps may come with a silicone or polytetrafluoroethylene (PTFE) septum, which creates a tight seal. Needles can pierce the septum because the elasticity of the material allows it to reclose.