The PTFE body of the cap creates a tight seal against the mobile phase reservoir. Tubing is connected using liquid and air tight fittings into the threaded connection ports. The air entering the container when solvent is withdrawn is filtered through a 120um PTFE particulate filter. A built-in check valve prevents solvent vapors escaping into the lab through the particular filter. All materials used are highly solvent compatible: Polypropylene (collar), PTFE (body) and FFKM (seals), making the caps usable in any LC laboratory.