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Posted: Wed Sep 30, 2009 5:46 am
by Bangkok34
I thought we are talking about headspace all the time
No. Don't have that but may well have to purchase if the acetonitrile extraction does give me joy. Trying that now and so far seems good. Thanks Peter.
Regards
Gung
Posted: Wed Sep 30, 2009 7:45 am
by Bangkok34
I now have a slight problem. To check whether I had some TEA left in the aqueous layer I injected this layer directly into my GC. This layer contained a lot of minerals and now I can hardly see any response even for the solvent peak.
I have replaced the liner and the septum but the problem persists. Does my detector now need cleaning?
Is it possible that the capillary column is blocked?
Thanks
Gung
Posted: Wed Sep 30, 2009 11:54 am
by gcguy
You could try a liquid/liquid extraction with a non-polar solvent. Adding even more salt would promote the efficency of the extraction. Or I wonder if there is a suitable SPE cartridge available?
Posted: Thu Oct 01, 2009 10:09 am
by Peter Apps
Hi Gung
Depending on injector and column tempratures and split ratio you might have deposited some muck in your column. If you remove the column form the gc and examine it against a bright light you might be able to see deposits inside it. If these are close to the inlet end just cut off the affected piece of column - this will not materially affect the resolution. If the deposits are further in you might have to try rinsing the column with methanol or even water, bust check first with the manufacturers that the column is likely to survive this.
A better way to check if there are any analytes left in the aqueous phase is to do another extraction with acetonitrile and then run that - the ratio between the first and second peak areas gives the % of analyte that is extracted each time.
Peter
Posted: Thu Oct 01, 2009 9:29 pm
by Bangkok34
Hi Gung
Depending on injector and column tempratures and split ratio you might have deposited some muck in your column. If you remove the column form the gc and examine it against a bright light you might be able to see deposits inside it. If these are close to the inlet end just cut off the affected piece of column - this will not materially affect the resolution. If the deposits are further in you might have to try rinsing the column with methanol or even water, bust check first with the manufacturers that the column is likely to survive this.
A better way to check if there are any analytes left in the aqueous phase is to do another extraction with acetonitrile and then run that - the ratio between the first and second peak areas gives the % of analyte that is extracted each time.
Peter
Thanks a lot Peter. Will try cleaning the column and also the double extraction.
Great suggestions.
Regards,
Gung
Posted: Sat Oct 03, 2009 2:33 am
by oscarBAL
Hello Gong; I think you could try SPME instead to buy a Head Space; using a very polar fiber; may some one else in this forum could tell you more about it.
Regards.
Oscar
Posted: Sat Oct 03, 2009 10:53 am
by Bangkok34
Hello Gong; I think you could try SPME instead to buy a Head Space; using a very polar fiber; may some one else in this forum could tell you more about it.
Regards.
Oscar
Thanks Oscar. I looked this up a few days ago and it sounds like this will indeed be suitable. I am trying to avoid purchasing more equipment though. We'll see what I can do.
Cheers
Alex
Posted: Sat Oct 03, 2009 10:57 am
by Bangkok34
Thanks Peter and everyone else who provided help and advice. I am now happy to report. That liquid-liquid extraction with MeCN (as per Peter's suggestion) works a treat. The 2nd extraction of the aqueous layer shows that the MeCN extract contains no detectable TEA or MeOH concluding that a single MeCN extraction is sufficiet.
Very pleased...
Thanks
Alex