Overview
Silicone rubber is the primary sealing material used in most chromatography autosampler vial septa. While silicone may appear similar across products, significant differences can exist depending on how the material is cured during manufacturing.
The curing method affects:
- Extractables and leachables
- Chemical stability
- Long-term performance
- Compatibility with trace-level analysis
- Suitability for HPLC, GC, and LC-MS workflows
Selecting the appropriate septum can help reduce contamination risks and improve analytical reproducibility.
Silicone Rubber Curing Technologies
Silicone rubber must be cross-linked, or cured, in order to develop the physical and chemical properties required for chromatography applications.
The two most common curing methods are:
Addition Cure (Platinum-Catalyzed)
Addition-cure silicone is produced using vinyl-functional silicone oligomers reacted with silicon hydride groups in the presence of a platinum catalyst.
Benefits include:
- Very low extractables
- No significant curing byproducts generated
- Excellent chemical purity
- Superior performance in LC-MS and trace-level analyses
- Consistent long-term stability
Because of the specialized catalyst and manufacturing controls required, this process is generally more expensive than peroxide curing.
Free Radical Cure (Peroxide-Catalyzed)
Peroxide-cured silicone uses organic peroxides and heat to initiate vulcanization and cross-link formation.
Characteristics include:
- Cost-effective production
- Broad use in routine chromatography applications
- Suitable performance for many HPLC and GC methods
However, peroxide curing may produce residual byproducts and generally results in a higher extractables profile compared to platinum-cured silicone.
MICROSOLV Septa Technologies
MICROSOLV offers both curing technologies to accommodate different analytical requirements.
AQR™ Septa (Advanced Quality)
AQR™ Septa utilize platinum-catalyzed silicone technology and are recommended for applications requiring maximum cleanliness and minimum background interference.
Ideal applications include:
- LC-MS analysis
- Trace-level quantitation
- Sensitive pharmaceutical methods
- Biomolecule analysis
- Environmental testing
Standard MICROSOLV Bonded Septa
Standard MICROSOLV bonded septa utilize peroxide-cured silicone and are well suited for:
- Routine HPLC applications
- General analytical testing
- GC analyses
- Quality control laboratories
These septa provide excellent performance for many common chromatographic workflows.
The Function of PTFE Liners
Virtually all chromatography septa incorporate a PTFE facing layer.
PTFE serves as a barrier between the sample and the silicone rubber and helps:
- Reduce contamination
- Minimize analyte adsorption
- Improve chemical compatibility
- Protect sample integrity
However, repeated autosampler needle punctures may eventually expose portions of the underlying silicone material, potentially increasing the likelihood of sample contact with the rubber substrate.
Comparative Extractables Profile
| Extractable | Platinum-Cured | Peroxide-Cured |
|---|---|---|
| pH Shift | 0.0 | -2.3 |
| Total Organic Carbon (TOC) | 2.63 µg/g | 62.73 µg/g |
| Residue | 13.3 mg/g | 10.51 mg/g |
| Siloxanes | 10,241 µg/g | 3,837 µg/g |
Selection Considerations
No single septum composition is ideal for every analytical method.
For example:
- Platinum-cured septa generally exhibit lower TOC levels and reduced pH impact.
- Peroxide-cured septa may exhibit lower siloxane content.
The most appropriate choice depends on:
- Analyte sensitivity
- Detection technique
- Regulatory requirements
- Method performance objectives
Evaluating the complete analytical workflow is often the best approach when selecting vial closure components.
Product Families Featuring These Septa
Available in:
- AQ™ Brand Autosampler Vials and Caps
- RSA™ Vials, Inserts & Caps
These product lines provide options for both routine chromatography and high-sensitivity analytical applications.
Conclusion
Although silicone rubber is used in most autosampler vial septa, the curing process can significantly influence analytical performance. Platinum-cured silicone offers exceptionally low extractables and is often preferred for LC-MS and trace analyses, while peroxide-cured silicone remains a practical and effective choice for many routine HPLC and GC applications. Understanding these differences helps ensure that vial closure systems are properly matched to analytical requirements and performance expectations.