[mir]

Do any of you have experience in using a syringe to take a gas sample from a gasbag? Please make a detailed procedure of how you do it.

I get only air when Im doing it, so thats why Im asking. I have made sure to open the vent completely. We have also a simple plastic septum fused in a silicontube, which makes a close connection between the vent and the outside. Then we use a 20 mL syringe with a "handle" of some kind which we can trap the sample inside while transporting it to the GC, where we open it and injects.

[JGK]

Are you collecting a sample into a gasbag the injecting part of it, if so you may be better off using a sampling bottle (taps at eagh end) where you can draw the sample through. the bottles also  have septum ports for sampling.

or

Taking a sample from a filled bag

In the latter, most commercial bags have a side arm with is opened and used to fill the bag intitially (then sealed) and an injection port septum which is used to remove samples (from the sealed Bag) for analysis etc.

20 mL seems an awfully large sample size for a GC. you may be better off with much smaller samples.  Also for a manual injection, a reproducible  injection technique is the key to consistent work.

[mir]

Sampling bottle? Kan you make a drawing?

We dont need to mind the amount of gas injected. The GC (Agilent 7890) have a loop, which holds 1 mL of sample, the rest is flushed out along with any helium from the last injection. A valve is shut on and the sample is flushed into the column(s) with helium. For this to work, we need pressurized containers or a syringe.

[JGK]

available from http://www.coleparmer.com/index.asp

[mir]

Nice!

I simply love glass equipment!

[wpenrose]

This is the method I use with 2 mil Tedlar sample bags:

First, you need a gastight syringe. They have a little valve at the base of the needle which closes when you twist the barrel, trapping the sample in the syringe.

I put a small square of invisible tape on the bag, and stick the needle right through the tape. Afterward, the hole is sealed with another layer of invisible tape.

The integrity of the bag is scarcely damaged, and the gas sample is being drawn from the bulk gas, not some subsample that happens to be trapped in a sampling valve.

Dangerous Bill

[JGK]

This is the method I use with 2 mil Tedlar sample bags:

First, you need a gastight syringe. They have a little valve at the base of the needle which closes when you twist the barrel, trapping the sample in the syringe.

I put a small square of invisible tape on the bag, and stick the needle right through the tape. Afterward, the hole is sealed with another layer of invisible tape.

The integrity of the bag is scarcely damaged, and the gas sample is being drawn from the bulk gas, not some subsample that happens to be trapped in a sampling valve.

Dangerous Bill

Most bags I use have a sampling port and the needle projects beyond this port into the body of the bag. As long as the bag is not overfilled, the syringe needle can vbe positioned close to the centre of the bag volume without the need to compromise the bag integrity.

[wpenrose]

Most bags I use have a sampling port and the needle projects beyond this port into the body of the bag. As long as the bag is not overfilled, the syringe needle can vbe positioned close to the centre of the bag volume without the need to compromise the bag integrity.

We generally used custom bags without a septum port (for economy). We did tests to make sure the tape was not interfering with our samples. But Tedlar is tough. We could make hundreds of penetrations without any sign of leakage, contamination, or tearing. Most bags ultimately failed near the fittings, whether a Jaco or some other fitting, and not due to the piercings.

One caution, never put the needle twice through the same hole.