Molded Thermogreen LB-2 Septa Durability

By: Robert F. Wallace, Gregory A. Baney, Reporter US Volume 28.1

Robert F. Wallace and Gregory A. Baney

bob.wallace@sial.com

Introduction

The injection port septa selected for gas chromatography (GC) use should exhibit low bleed, resist leaks, and be easy to penetrate. Molded Thermogreen LB-2 septa have all these characteristics. Using the same exclusive rubber formulation as the traditional Thermogreen LB-2, molded Thermogreen LB-2 septa allow for stricter tolerances of both diameter and thickness, resulting in much easier installation and better sealing. A previous article discussed the low bleed characteristics of molded Thermogreen LB-2 septa (1). This article will focus on their resistance to leaks.


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Durability Requirements

A GC septum should resist fragmentation. This is because septum fragments in the inlet liner bleed (observed as extraneous peaks) and adsorb active sample components (causing loss of analyte response). Molded Thermogreen LB-2 septa are specially engineered to offer excellent resistance to fragmentation. With its high elasticity, molded Thermogreen LB-2 septa ensure that multiple injections can be obtained with a wide range of needle compatibility. In fact, the entire Thermogreen LB-2 family is widely accepted as the industry standard in GC septa because of their great durability.

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Puncturability Test

As a measure of durability, a molded Thermogreen LB-2 septum with injection hole was subjected to repeated injections. Column head pressure and carrier gas linear velocity/flow rate were monitored throughout the test to determine if the septum developed a leak. An autosampler was used for the test, ensuring that the syringe needle (tapered 23s-26s gauge) punctured the same location repeatedly. Figure 1 shows chromatograms from the initial run and after 2100 injections. As demonstrated, no artifacts were present in either the initial or final runs to indicate any problems with the chromatography. Additionally, retention, head pressure, and column flow remained constant, indicating that a leak-free seal was maintained.

Figure 1. Molded Thermogreen LB-2 Septum Durability Test (28471-U)


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Conclusion

The quality traits to look for in a GC septum are low bleed, resistance to leaks, and easy penetration. The strict tolerances of the mold used to manufacture molded Thermogreen LB-2 septa result in septa that are easier to install and consistently fit better. These septa exhibit an ultra low bleed profile, are temperature stable to 350 °C, are very resistant to both slivering and coring, and have a high puncture tolerance.

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Materials

     

References

  1. M.D. Buchanan, “NEW! Molded Thermogreen LB-2 Septa” The Reporter 25.3 (2007) p. 15.

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