May 28, 2020 · HPLC autosampler vial cap is Polypropylene screw cap and snap cap. At the same time, Aijiren can also supply crimp top aluminum cap for autosampler vial. Polypropylene Screw Cap with Septa - Polypropylene screw cap with precision-fit septa provide an evaporation-proof seal. Screw caps provide an inert, airtight seal and direct puncture-access