Mar 22, 2020 · Chromatography vial closures also referred to as seals, are the combination of a cap and septa. To ensure reliable analyses, it is therefore important that all closures are inert and uncontaminated as well as the vial itself. 1. Types of Autosampler Vial Closures . HPLC / GC Vials are available in three closure types; crimp, snap and screw cap.