GC vials are used to hold the sample that is being tested. These vials are always sealed and gas-tight to ensure none of the sample is allowed to escape. The middle of the vial cap contains a septa, which is typically 5 to 8 mm wide and made from Silicone, Rubber, Butyl, Teflon, Viton, or PTFE. It is these materials that are punctured by the GC syringe and allows the chromatograph to safely capture the sample without releasing any of it from the vial. The septa materials can also be layered on top of each other to form a whole septa.
Septas are usually chosen based in gas chromatography on how many repeat injections the syringe must make. PTFE/silicone/PTFE is always the best option for resealability when applications require a longer time between injections. PTFE/silicone is also a good option for use with repeat injections – it is most commonly used in HPLC and GC analysis. PTFE/red rubber septa are not recommended for multiple injections or for samples that need to be stored for a period of time for further analysis.
GC vials also can have different means of attaching the vial cap to the vial, depending on needs of the application. Vials usually accept crimp caps, screw caps, or snap caps. As their names suggest – screw caps screw onto the GC vial; crimp caps are crimped down manually or with a crimper to form a complete seal; and snap caps are snapped onto the vial.
GC vials are made from amber or clear borosilicate glass, with amber glass being used for light-sensitive samples. Borosilicate glass has great chemical and thermal resistance, as well as optical clarity, making it ideal for GC glassware.
The most common GC vial sizes are 12 x 32 mm vials and 15 x 45 mm vials. Depending upon the vial manufacturer, a 12 x 32 mm vial may also be referred to as a 1.5 mL vial, a 1.8 mL vial, or a 2.0 mL vial.