The temperature range for silicone rubber used in autosampler vial caps is -55°C to 220°C but you should note that the polypropylene, used in the caps, structural integrity may be lost at these high temperatures. If the silicone rubber septa is used in an aluminum cap, that should be okay even at 220°C.
Also, at higher temperatures than noted above, silicone rubber can become hard, almost to the point of being brittle. However, most autosamplers, including Headspace instruments, do not use temperatures high enough to cause this to happen.
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