Sep. 9th, 2022
The septum you choose for your autosampler vial can impact sample evaporation, sample security, needle bending and blockages, and instrument downtime. Don’t let the complexities of septa selection slow you down.
Septa Selection Tool
The Septa Selection Tool recommends the best septa by answering a few simple questions, such as:
HPLC, UHPLC, or GC?
Screw thread caps, crimp top caps, and snap-it caps?
Autosampler needle type & tip diameter?
Slit or non-slit design?
Solvents and temperature that the septa will be exposed to?
Septa Decision Tree
The Septa Selection Tool makes use of the chart below to select a septum that will help prevent contamination and avoid damage.
Four Important Points you need to Consider when Choosing the Suitable Septa:
Each instrument vendor uses different injector needle types and for some instruments, having pre-slit septa, or choosing a material with a lower shore (hardness) value will help reduce the chances of needle issues, such as needle bending.
2. Compounds of interest
If your compounds are volatile then choosing septa that will provide a tight seal is key to preventing compound loss. Our Advanced Vial Closure System (AVCS) caps remove subjectivity around achieving the optimal seal compression when closing a vial.
Some solvents that are commonly used for HPLC, UHPLC, and GC experiments can impact septa integrity.
If you need to place a capped sample vial in a high-temperature environment, you will need to consider septa materials that can withstand high temperatures.
Septa are made from different materials. See below for definitions and uses of different types of septa materials.
They are used primarily for routine analysis in gas chromatography. Offers moderate ability to reseal and good chemical inertness. Not recommended for multiple injections or holding samples for further analysis. PTFE is a protective layer that once broken exposes rubber to chemical attack.
PTFE/red rubber: Low rubber durometer allows needle penetration. A popular and economical septum for general GC purposes.
PTFE/rubber: Harder grade of rubber for use with piercing needle. Most popular and economical septa for general GC purposes.
Pre-slit PTFE/red rubber: Pre-slit, high-quality red rubber with a thin (0.003") layer of PTFE. For applications using a very thin-gauge syringe needle or in instances when a vacuum may form in the vial.
High-quality, silicone rubber laminated to PTFE. Use when excellent resealing qualities are a must. Septum resists coring and is recommended when multiple injections are required. Preferred septa for use in liquid chromatography applications.
PTFE/silicone: A very pure soft silicone laminated to PTFE. Septum resists coring and is recommended for instruments with fine gauge needles. Also recommended for LC-MS and GC-MS due to high purity.
PTFE/silicone/PTFE: A layer of PTFE on each side of medium hardness silicone. Most resistant to coring with above-average resealing characteristics. Recommended for most demanding applications such as trace analysis, longer time between injections, or for internal standards. Use any autosampler using large diameter, blunt-tip syringe needles.
Pre-slit PTFE/silicone: Pre-slit, high-quality pure white silicone faced with PTFE. For applications using a very thin-gauge syringe needle or in instances when a vacuum may form in the vial.
PTFE and Fluoropolymers
Very good chemical resistance and used as a protective layer for less resistant elastomers.
Butyl Rubber/chlorobutyl Rubber
An economical choice for low temperature (< 125°C) or low-pressure applications. Not suitable for alkanes, benzene, chlorinated solvents or cyclohexane without a protective PTFE layer.
Excellent septa choice for volatiles with very low background peaks and low permeability. Also ideal for alcohols and aqueous samples. Good resealing characteristics and resistance to coring.
Natural PTFE/blue silicone: Best septa choice when temperatures are over 125°C.
Natural PTFE/red silicone: High temperature formulated seal with a low bleed. Best septa choice when temperatures are up to 300°C.
Blue silicone/red PTFE: Thin 1.4 mm seal with PTFE face. Resealing capability is limited due to the thinner silicone layer.
Aluminum/white silicone: Reflective aluminum face protects the silicone seal. The white silicone is suitable for use up to 170°C.
Aluminum/red silicone: Reflective aluminum face protects the silicone seal. The red silicone is suitable for use at temperatures up to 250°C.
Blue silicone/natural PTFE: Soft silicone with clean formulation for minimal interference. Thinner seals are suitable for solvent washing, solvent extraction, and solid phase microextraction (SPME) applications with some resealing. Not for direct headspace applications.
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