Polypropylene screw cap with septum-The polypropylene screw cap with septum provides an anti-evaporation seal. The double layer includes silicone and PTFE. The silicone septum can be injected multiple times. Screw caps lined with PTFE are used for organic samples. The screw cap provides an inert, air-tight seal and can be directly pierced through the sample with a syringe needle.
