Don’t let your septum be the cause of injection failure

The septum you choose for your autosampler vial can impact sample evaporation, sample security, needle bending and blockages, and instrument down time. Don’t let the complexities of septa selection slow you down. Use the simple online Thermo Scientific SureSTART Selection Guide to find the right septa and vial for your analysis.


Thermo Scientific SureSTART Selection Guide


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.

Multiple injection?Temperature?Thin, fragile needle?Blunt, thick needle?Critical analysis?Low coring?
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Good resealability required-40°C up to 120°C-40°C up to 110°C-60°C up to 200°CSoft and thin septa requiredSlit/pre-cut liner as penetration aid (HPLC)Very clean liner requiredDouble-sided PTFE laminated liners required
Arrow downArrow downArrow downArrow downArrow downArrow downArrow downArrow down
Natural rubber/TEFNatural rubber/TEF; Butyl/PTFERed rubber/PTFESilicone/PTFEe.g. Silicone/PTFESilicon/PTFE, slitSilicon/PTFEPTFE/Silicone/PTFE

Which septum do I need for my autosampler vial?

When selecting which septa is right for your experiments, it is important to consider the:


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.

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 the septa integrity.


If you need to place a capped sample vial in a high temperature environment, then you will need to consider septa materials that are able to withstand high temperatures.


Septa materials & properties

Septa are made from different materials. See below for definitions and uses of different types of septa materials.

Rubber septa

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 protective layer that once broken exposes rubber to chemical attack.

PTFE/red rubber – AC6, 6RT1

Low durometer of rubber allows ease of needle penetration. A popular and economical septum for general GC purposes.

PTFE/rubber – AC7, 8RT1

Harder grade of rubber for use with piercing needle. Most popular and economical septa for general GC purposes.

Pre-slit PTFE/red rubber – 8RT1X

Pre-slit, high quality red rubber with a thin (0.003") layer PTFE. For applications using a very thin-gauge syringe needle or in instances when a vacuum may form in the vial.

Silicone rubber septa

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 – ST1, ST15, ST18, ST2

A white medium hardness silicone with red PTFE protective layer available in a range of thickness.

PTFE/silicone – ST101, ST14

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 – ST143, ST144

A very soft silicone laminated to PTFE. Use with flexible needle.

PTFE/silicone/PTFE – TST1, TST11

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 with any autosampler using large diameter, blunt-tip syringe needles.

Pre-slit PTFE/silicone – ST1X, ST101X, ST14X

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.

PTFE – T, T02

For single injections and short sample cycles. This type of septa is not resealable.

Viton – V1

Viton provides the best chemical resistance with limited ability to reseal. Recommended for chlorinated solvents. Due to Viton’s intrinsic hardness, these septa are not suitable for finer-gauge syringe needles.

Integral plastic seal

Moulded as part of the cap.

Polyethylene – PE, Polypropylene – PP

Chemically resistant but for one time use only with no ability to reseal. Free of fluoropolymer coating, so suitable for PFOA analysis. 20 mm seal selection for headspace and sample preparation applications.

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.

Grey bromobutyl stopper – B3P

Does not provide PTFE barrier. Use for gas sampling due to low permeability.

Black chlorobutyl – CB3

Does not provide PTFE barrier. Use for gas sampling due to low permeability.

Grey bromobutyl/black PTFE – CBT3

Has PTFE barrier that makes it suitable for work with general organic solvents with low gas permeability.

Grey PTFE/black bromobutyl moulded – CBT3B

A specially moulded seal with a PTFE insert. Sealing surface of Butyl and PTFE affects a more positive seal than non-PTFE-faced septa. Ideal choice for temperatures below 125°C. Good sealing characteristics, excellent resistance to most solvents with reduced coring and high puncture tolerance. PTFE provides increased chemical resistance.

Silicone rubber

Excellent septa choice for volatiles with very low background peaks and low permeability. Also ideal for alcohols and aqueous samples. Good resealing characteristics and resistant to coring.

Natural PTFE/blue silicone – ST3, ST201

Best septa choice when temperatures are over 125°C.

Natural PTFE/red silicone – ST3HT

High temperature formulated seal with low bleed. Best septa choice when temperatures are up to 300°C.

Blue silicone/red PTFE – ST144

Thin 1.4 mm seal with PTFE face. Resealing capability limited due to thinner silicone layer.

Aluminum/white silicone – AS3

Reflective aluminum face protects the silicone seal. The white silicone is suitable for use up to 170°C.

Aluminum/red silicone – ASH3

Reflective aluminum face protects the silicone seal. The red silicone is suitable for use at temperatures up to 250°C.

Blue silicone/natural PTFE – ST101

Soft silicone with clean formulation for minimal interference. Thinner seal suitable for solvent washing, solvent extraction, and solid phase microextraction (SPME) applications with some resealing. Not for direct headspace applications.

Freezer bungs – 2FB3

Butyl bungs for sealing of lyophilized products. Compatible with low storage temperatures and low gas permeability.

PTFE/silicone ring – LLX

Thin PTFE layer with sealing ring to give secure closure for strong solvents. For use in liquid extraction or SPME stage during sample preparation. Does not reseal. Single use only.


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