GC Injection Port Septa: Use, Maintenance, Storage and Handling

GC Performance Tip, Reporter Vol. 29.2

A GC septum is located at the top of the injection port and serves two functions:
1) providing a leak-free seal to maintain carrier gas pressure inside the system
2) handling repeated puncturing by a syringe needle for sample introduction purposes without severe coring or leaking.

Temperature-Programming: When performing temperature-programmed analyses, you may observe ghost peaks or a baseline rise not traceable to the sample or to column bleed. These disturbances are often caused by septum bleed. Volatile materials from the septa can accumulate at the head of the column during the cool-down portion of the program. When the column is heated for the next sample, these accumulated volatiles are eluted, producing peaks, a general baseline rise, or both.

Routine Maintenance: To reduce the risk of leaks and contamination, injection port septa should routinely be replaced. Change the septum daily, especially if the instrument is in heavy use. Repeated use of the same septum may resultin increased coring, resulting in a leak. Septum fragments in the inlet liner can also lead to ghost peaks and/or loss of response due to adsorption of analytes as they pass through.

Storage and Handling: Septa can become contaminated by volatile compounds in the room air, or by finger oils. To ensure cleanliness, it is recommended that septa be stored in their shipping container with the lid securely closed, and that clean forceps be used for handling the septa during installation.