When should I replace the red septa if it has been pierced with a GC needle?

The red septa can be used repeatedly during a study as it reseals when the needle is withdrawn. When pierced during gas sampling, it is important to use a small gauge needle and avoid puncturing the membrane in the same location. The red septa are found in Septa Bottles (Part #'s: 7120, 7130, 7131, and 7132) and septa replacements are available in packs of ten (Part #: RF35).

With a PTFE layer on both faces, it offers very low CO2 permeability compared to a standard silicone septum and, when new, contributes only about 0.001psi loss per hour through permeation. It is recommended that used septa be replaced before starting a run as CO2 permeation increases slightly each time a septum is pierced with the GC needle. Each penetration of a 10 µL (0.017" diameter) GC needle the CO2 permeation increases by about 0.001 psi/hr. So, when septa bottles are used in a study, use a septa bottle for your blank as well and pierce the septum on the blank with the needle as you do the rest of the samples to factor out the increased CO2 permeation. For further discussion on the use of a blank, refer to the RF Getting Started Guide.