Do You Really Know How To Choose The Right Septa for Sample Vial?
Commercially available septa are generally divided into three types, ordinary type (temperature resistant to 200°C), high quality type (temperature resistant to 300°C), and high temperature type (temperature resistant to 400°C). The better the high temperature resistance or aging resistance and the longer the life, the higher the price of course. The choice can be determined according to the actual analysis conditions and requirements.
The conventional analysis laboratory (vaporization temperature does not exceed 300°C) can choose high-quality septa, and it is recommended to choose high-temperature septa for high-temperature gas analysis. As for how often to replace the septum, it depends on the nature of the analyzed sample and the analysis conditions. Routine testing laboratories generally change one every day. It is recommended that the continuous use time of a septum should not exceed one week. of course, an experienced operator can judge whether it needs to be replaced based on experience.
From the material of the septa, it can be PTFE, PE, and PP septum, among which the PTFE has different types. We summarize the features for your reference.
1. PTFE septum
The solid 0.010″ thick PTFE layer has excellent chemical inertness and can withstand the most corrosive solvents. The membrane is convenient for most needles to penetrate. The PTFE septum is not resealable and must be used for short injection intervals or single injection analysis.
2. PTFE/natural red rubber
PTFE natural red rubber gasket is moderately priced and has good chemical properties, suitable for GC and HPLC. The repeated sealing performance is good, and it is an ideal choice for multiple injections, but the penetration performance is worse than PTFE/RR.
3. PTFE/red synthetic rubber septum: (PTFE/RR)
PTFE/red rubber septa are the most popular and economical choice for general GC and HPLC applications. The PTFE/red rubber septum has moderate re-sealing properties and excellent chemical inertness before penetration. It is mainly used for routine gas chromatography analysis using FID, TCD, and FPD detectors. The red rubber has low hardness and is easily penetrated by a needle, even with a fine gas chromatography needle. But, it’s not suitable for multiple injections or samples retaining for further analysis.
Note: The high-quality red rubber with a PTFE layer thickness of 0.003″. The high-quality medium hard red rubber with a PTFE layer thickness of 0.015″.
4. PTFE/high performance red rubber
PTFE red rubber is a high-purity red synthetic rubber septum that can be used in high-sensitivity detectors such as ECD or NPD to reduce the background noise level of GC. The repeated sealing characteristics of PTFE red rubber are similar to those of PTFE/red rubber and are pre-assembled with aluminum caps.
5. PTFE/silicone septa: (T/S)
With high quality, low background noise/blank value, and 100% synthetic pure silicone septa, it is suitable for all types of chromatographic applications. The thickness of the PTFE layer is pressed down to 0.005″, high purity, high inertness, excellent resealing characteristics, and can withstand multiple punctures.
PTFE/Silicone diaphragm is a good choice for most high performance liquid chromatography and gas chromatography applications, PTFE/silicone septa can meet its re-seal and purity requirements, cleaner than natural or red rubber. There are many different hardness options to meet the requirements of different types of needles.
6. Pre-opened PTFE/silicone septa
The center hole of the high-purity silicone layer of the PTFE/silicone septum is pressed with a 0.005″ thick PTFE layer, which facilitates needle puncture and releases the vacuum when a large number of samples are drawn out. The chromatographic characteristics are similar to those of the non-pre-opened septum. Ability is slightly weaker. It is strongly recommended to use pre-opened septa for autosamplers with smaller needle specifications. Adhesive bottle cap: The cap is equipped with an electrolytically bonded PTFE/silicone septum.
7. PTFE/silicone/PTFE septum: (T/S/T)
The septum is made of high-purity, medium-hardness silica gel with a layer of 0.003″ thick PTFE on each side to avoid slagging while still maintaining good resealing properties. T/S/T septa are recommended for two injections The most important applications such as long intervals or the use of internal standard methods, such as trace analysis, etc. The performance of the T/S/T septum is suitable for use with autosamplers with large diameter blunt needles.
8. Polyethylene (PE) septa/one-piece blown film cap/cap/stopper:
The polyethylene septa are chemically resistant and are usually molded into a single bottle cap. The thickness of the penetrating surface of the needle is 0.01″, which is suitable for fine gauge needles. The polyethylene septum cannot be resealed and is only suitable for a single injection.
9. Polypropylene (PP) Septa/Overall blown film cap/cap/stopper:
The polypropylene septa are chemically resistant and can be divided into a single bottle cap or a 0.01″ thick septum. The thickness of the penetrating surface of the needle is 0.01″, which is suitable for fine gauge needles. The polypropylene septum is not resealable and is only suitable for a single injection.