Chromatography Forum

We are using a HP GC 5890 with FID for sampling LPG. We are using a liquid sampling valve. It was workinf fairly good. But the reproducibility is not OK. We are discussing what is the best method for injecting the sample. We are using a regulator at the entrance of the sample. We are using a normal ball valve regulator but I think that the best would be a double stage regulator? What do you think? WE have a regulation valve at the waste end of the valve.
We are sampling the following way:

1. First valve in sampling position
2. open the sampling valve and regulating the pressure to 50 psi
3. open the waste valve and regulating to get the same 50 psi
4. Wait 30 seconds
5. Inject

We have tried many forms of injection and this was the one that gave us the best results.

Do you know where can I find the best method for sampling LPG?

What is "LPG"?

If it's a liquid sample, I wouldn't regulate it. I would plumb right from the cylinder (or quick connect) to the LSV. Then I would add a small section of opaque/clear poly tubing downstream of the LSV and upstream of a needle valve. Then attach the cylinder, close the needle valve, then open the cylinder valve all the way. Now crack the needle valve and use the clear tubing to ensure that you have a liquid full sample loop.

I think he means liquified petroleum gas. Where I work, we have so many three letter abbreviations, that those are called TLAs. Really. Every time I have to go to a #$%#@$$^&&*^$## meeting I hear a zillion that I have no idea what they mean. But many yuppies just assume that everyone knows them all.

Apparently there's a secret spreadsheet that lists them, but it's password protected by a TLA.

Yes LPG means Liquid Petroleum gas and this is the propane gas that we use in the kitchen for coocking.

If it's a liquid sample, I wouldn't regulate it. I would plumb right from the cylinder (or quick connect) to the LSV. Then I would add a small section of opaque/clear poly tubing downstream of the LSV and upstream of a needle valve. Then attach the cylinder, close the needle valve, then open the cylinder valve all the way. Now crack the needle valve and use the clear tubing to ensure that you have a liquid full sample loop.

Thank you for your answer, we will try it.