Why septum quality matters
Temperature limit
The temperature set on the GC for the injection port is not the same as the actual septum temperature. Most injection ports have cooling fins on the septum nut that cool the septum. At a set port temperature of 400°C, the actual septum temperature is usually no higher than 280°C. One centimetre deeper into the port, 400°C is reached. This means that in most cases the septum is under less stress than the set temperature suggests, but the right temperature class still matters.
Septum bleed
The classic method of making low-bleed septa is intensive polymerisation and crosslinking of silicone, followed by heating to drive out residues. However, this results in a hard septum with disadvantages for needle penetration and resealability. Brown solves this with a unique conditioning process that minimises bleed without compromising the softness of the silicone. Once punctured, the internal components of Brown septa remain stable: no bleed after puncture.
Coring
Coring occurs when the needle cuts small particles from the septum that end up in the needle or column. The excellent softness of Brown septa at high temperature greatly reduces the risk of tearing. This softness also improves resealability and extends service life. Brown recommends using a needle guide to concentrate punctures in a small area and further extend septum life.
Standard GC septa (156xxx series)
Made of 100% pure premium silicone rubber. Available in three temperature classes, recognisable by colour:
- Green: max 300°C
- Blauw: max 350°C
- Rood: max 400°C
Available in four diameters: 9.5 mm, 11.0 mm, 12.5 mm and 17.0 mm. Per 25 pieces.
| Cat. no. | Colour | Diameter | Max. temp. |
|---|
| 156003 | Green | 9,5 mm | 300°C |
| 156018 | Blue | 9,5 mm | 350°C |
| 156015 | Red | 9,5 mm | 400°C |
| 156004 | Green | 11,0 mm | 300°C |
| 156019 | Blue | 11,0 mm | 350°C |
| 156016 | Red | 11,0 mm | 400°C |
| 156005 | Green | 12,5 mm | 300°C |
| 156020 | Blue | 12,5 mm | 350°C |
| 156017 | Red | 12,5 mm | 400°C |
| 156031 | Green | 17,0 mm | 300°C |
| 156036 | Blue | 17,0 mm | 350°C |
| 156035 | Red | 17,0 mm | 400°C |
Ultra-low bleed GC septa (160xxx series)
The ultra-low bleed series is specifically for applications where a minimal septum background is essential, in particular GC/MS and other detection techniques that are sensitive to interfering peaks. All septa in this series are:
- Conditioned for ultra-low bleed
- Soft and strong premium silicone
- Produced to order for maximum freshness
- Marked with the production date on the packaging
Practical benefits:
- No interfering peaks in the chromatogram
- Reduced contamination of column and detector
- Easy needle penetration and good resealability
- Easy stock management thanks to date marking
Ultra-low bleed, standard (max 325°C, purple)
Available with and without guide hole. A guide hole helps centre the needle and extends septum life by concentrating punctures in one point.
| Cat. no. | Diameter | Gidsgat |
|---|
| 160500 | 9,5 mm | No |
| 160501 | 10,0 mm | No |
| 160502 | 11,0 mm | No |
| 160503 | 17,0 mm | No |
| 160505 | 9,5 mm | Yes |
| 160506 | 10,0 mm | Yes |
| 160507 | 11,0 mm | Yes |
| 160508 | 17,0 mm | Yes |
Ultra-low bleed high temperature (max 400°C, red)
For GC methods with high injection port temperatures, such as analyses of heavy hydrocarbons, polymer residues or flavourings.
| Cat. no. | Diameter | Gidsgat |
|---|
| 160510 | 9,5 mm | No |
| 160511 | 10,0 mm | No |
| 160512 | 11,0 mm | No |
| 160513 | 17,0 mm | No |
| 160515 | 9,5 mm | Yes |
| 160516 | 10,0 mm | Yes |
| 160517 | 11,0 mm | Yes |
| 160518 | 17,0 mm | Yes |
Ultra-low bleed high temperature for Shimadzu (max 400°C, red)
Special version tailored to Shimadzu GC injection ports.
| Cat. no. | Colour | Max. temp. |
|---|
| 160520 | Red | 400°C |
Which septum should you choose?
| Situation | Recommended series |
|---|
| Routine GC analysis, injection port up to 300°C | Standard green (156003 series) |
| Routine GC analysis, injection port up to 350°C | Standard blue (156018 series) |
| High port temperature up to 400°C | Standard red (156015 series) |
| GC/MS, low background required, up to 325°C | Ultra-low bleed purple (160500 series) |
| GC/MS, low background, high temperature up to 400°C | Ultra-low bleed red (160510 series) |
| Shimadzu GC, low background, high temperature | Shimadzu ultra-low bleed (160520) |
| Frequent injections, limit needle wear | Version with guide hole (160505 series) |
The right diameter for your GC
The septum diameter depends on your GC manufacturer and injection port type. The most common sizes are:
- 9.5 mm: broadly compatible, including Agilent, Thermo, Perkin-Elmer
- 10.0 mm: including Shimadzu-specific ports
- 11.0 mm: including certain Varian and older Hewlett-Packard models
- 12.5 mm: less common, specific port types
- 17.0 mm: larger ports, including certain Perkin-Elmer and Thermo models
Not sure which size fits your GC? Contact Inacom for advice.