How to Choose the Right Septa for Your Autosampler Vial Closure

When performing LC and GC analysis, you’ll need something to store and transport your samples prior to injection. Chromatography vials are the most common vessel, but come in a variety of shapes and sizes (we discuss this in depth in a previous autosampler vial blog). Not only that, but there are many different closure styles with varying septa materials as well. In this blog, we’ll discuss some of the different septa materials available and the reasons why some may be better for certain applications than others.

Common Septa for LC Vials

The most common vial type for liquid chromatography are screw thread vials and closures. The most common septa used in screw thread closures is a PTFE and silicone combination (commonly shown as PTFE/Sil). PTFE/Sil is a great choice for multiple injections due to its resealing capability. It’s also very common to see PTFE/Sil septa with a slit, which is ideal for instances where the autosampler needles tends to “stick” to the septa and pull the vial up with the needle. For an economical septa option, polyethylene (PE) septa are a common choice amongst LC users with a snap seal vials and closures.

Common Septa for GC Vials

Since gas chromatography typically involves relatively volatile compounds, a tight sealing closure is crucial. A crimp style closure is most commonly used for GC applications, and typically the aluminum crimp caps are paired with a PTFE and rubber combination (PTFE/rubber) septa. The combination of PTFE with a rubber compound offers a great seal within the aluminum cap.

Minimizing Background Noise from Septa

Different analyses require varying amounts of sensitivity, and sometimes the traditional septa options aren’t ideal for certain applications. If you’re experiencing any background interference in your GC applications, specially formulated rubber compounds such as our Seal 2000 septa can be used in place of natural rubber to minimize any noise. Likewise, we offer Mass Spec Quality (MSQ) septa for our screw thread closures, which many of our mass spec customers pair with low adsorption vials to achieve little-to-no background interference.

On a related note, some applications such as PFAS analyses can be contaminated if any PTFE is used in the flow path of the instrumentation. Therefore, using PTFE-lined septa in the vial caps is not an option. We recommend a polypropylene snap top vial and a corresponding snap top vial with PE septa. For a more complete comprehensive list of PTFE-free consumables, check out our guide for reducing PFAS contamination on our resources page.

Storage Vials

One other septa material worth noting is the septa typically used in solid top storage caps. Most commonly, you’ll find storage closures to be lined with PTFE/F217. F217 is a polyolefin foam extruded between two layers of polyethylene, usually 0.050” thick. The F217 allows the closure to be torqued down with 20 lbs of foot pressure, and once the pressure is backed off, the foam comes back to almost 100% of its original shape, which gives a good, repeated seal. This is great for storage and allowing the closures to be opened and closed many times.

Compatibility of Solvents

While many typical chromatography solvents are compatible with most of the standard septa materials, here is a list of materials and their compatibilities/incompatibilities with various solvents:

If you have any questions regarding vials, closures, or septa for your specific applications, please reach out to our product specialists for information.