Chromatography Forum

The contamination (if there is any) could be anywhere in the rather complicated sample path. If you do not have the deactivated tubing option it might be worthwhile doing a steam clean - if I remember correctly there is a procedure in the manual - before you start replacing things. If you do have deactivated plumbing the steam clean will activate it in short order.

How are you connecting the transfer line to the inlet ?

Peter

YES, our agilent rep showed me how to do a steam clean, and although it greatly reduced the problem, it didn't completely eliminate it. I decided to have the sample loop replaced. I have been with this company for 5 years, and to my knowledge, it has never been replaced. I think this may solve the problem. stay tuned.

Hi

You may not have to toss your previous loop, cleaning it in an ultrasonic bath with water/ethanol for a short period may be enough to clean it up. Have worked for us (goes for the HS needle as well).

We're under service contract, we may as well get our money's worth. hehe I had the loop replaced, and he also recommended that I up the vial pressure to about 13 or 14. He also replaced the vent line. That made a huge difference. I looks like things are back to normal here. Thanks for all the tips guys.

We have a G1888 and 7890A. We have been seeing ghost peaks for some time now. We replaced the inlet liner, tried new vials, new/ different caps, trimmed the column, replace the sample probe, and recently replaced the entire HS system...
The first injection of air made using the new system had the peaks that we had been seeing, however, in very small amounts that were at less than 10:1 signal to noise. I ran my usual sequence ( 6 injections of residual solvent std) and an air afterwards and the peaks size looked the same.
The GC/HS system was shut down for 2 days. I brought the system back up, ran an air and the got large peaks we had been seeing before the HS was replaced. We have elimiated the GC by doing a GC start - Clean baseline.
We ran uncapped vials and got a clean baseline. Would this be because the system did not build any pressure from the vial being uncapped to be able to push the solvents from where they are clinging? Or could this suggest that the caps are causing the contamination?
The peaks can be gotten rid of by steam cleaning or by baking the loop/transferline/inlet/column while doing a standby purge for ~ 30 min, however, they just keep coming back and this is not something we feel that we should have to do after every sequence. We have data from 2 other labs using the same validated method, same standards, same system and they have not had this problem. Any suggestions would be appreciated. Thanks for reading!

It sounds like the source of the peaks is the carrier gas.

You replace the HS system and it takes a while for the contamination to pass through the instrument.

You clean up the system and it is ok, but then it returns.

Dirty traps or cylinders or gas regulators could be the problem.

best wishes,

Rod

Thanks Chromatographer1 for your response.

Ends up the peaks that we are seeing are acctually coming from the air (thankfully, at levels calcualted to be very well below the TLV for that compound)

People don't believe me when I told them I could see benzene and toluene in HS samples prepared as trucks passed by my building with the windows open.

Thanks for sharing the solution. It is nice to know the end of the story.

Rod

kmiller-

Just wondering how you were able to confirm the peaks were coming from the air in the lab? Purge a vial with carrier, cap, and run?

I've told everyone that I work with to check what other people are working on before starting their headspace preps. If anyone is working with a solvent you will be looking for, move to another spot or ask the other person to move into a hood. Moving yourself to a hood might not work, as the hood is going to pull lab air through your workspace.

-Greg

Your right, taking a sample in the hood can be even worse then out of the hood. I like to take a blank air sample wherever the sampling/preparation is done. Before i would just completely avoid preparation if any solvents were open.
We sent some of our vials capped to one of our other labs in a different facility. When they obtained the same results as we were seeing we were able to rule out our instrument. That left us with either our cap/vial assembly or air to be the source. The other lab sent us capped and uncapped vials so that we could test. We placed all the vials in an inert environment to avoid contamination with our lab. Ran one of their capped vials, one of their uncapped vials was exposed to our lab, and another was taken outside of the building. The only one with peaks that we had been seeing was the one that was exposed to our lab. Prior to any of these analysis we had placed several vials around the building and ran them and saw the peaks so we thought that the contamination was the instrument ( this confimed that our air is the source)
We did purge some of our vials with gas and this did reduce the areas, however, we also saw reduced areas or no peaks when sample and/or diluent was added. So we did not know if maybe the vials were contaminated and it was being masked by the gas... or what was going on.

I hope that this helps anyone that is having a similar issue.

People don't believe me when I told them I could see benzene and toluene in HS samples prepared as trucks passed by my building with the windows open.

Thanks for sharing the solution. It is nice to know the end of the story.

Rod

I had a whole day's samples contaminated because tar was being sprayed on an airport apron about 500 m away - low detection limits work both ways !!

Peter

People don't believe me when I told them I could see benzene and toluene in HS samples prepared as trucks passed by my building with the windows open.

Anyone who has done enough headspace work has seen such things...

I was trying to measure residual methylene chloride in drug product for an IV formulation (so looking for low levels) by headspace and it in seeing in the air blanks... Turned out people were using it in the next lab over.

- Karen