Polypropylene caps are chemically inert and suitable for most chromatography applications Shop Fisherbrand™ 8mm PP Screw Seal, Black, Closed top, 8-425 thread, Fisherbrand™ 8mm PP Screw Seal, Black, Closed top, 8-425 thread, Assembled septum: Autosampler Vial Caps and Closures Autosampler Vials, Caps, and Closures | Fisher Scientific