We regularly analyze AAs in liquid ethyl acetate (no more than 4ul at once), and we leave the backflush on for 550 sec post injection to
avoid a solvent peak (we have a 60m column). Hope that's helpful.
On Jun 27, 2012, at 14:26, Geert Van Biesen <[log in to unmask]
> are you injecting pure (liquid) ethyl acetate? In that case you generate a huge
> amount of CO2 and H2O and you are very likely overloading the system (hence the
>> 50 V m/z 44 peak). Why don't you try sampling from the headspace: add about
> 100 microliter of ethyl acetate into a sample vial so that the syringe only
> draws up vapour, and see how that works out. If you would use ethyl acetate as
> solvent for your samples, make sure you have the backflush on long enough to
> divert it from the oxidation reactor.
> Good luck,
> Geert Van Biesen, PhD
> Research Laboratory Associate
CREAIT - Stable Isotope Lab
> Memorial University of Newfoundland
> [log in to unmask]
> Quoting Matheus Carvalho <[log in to unmask]
>> Dear all,
>> we are trying to measure amino acids here, and there is a problem that I
>> cannot understand.
>> I installed two 25m columns in the GC oven, one coupled to the other, so that
>> the total length is 50m. I put a new oxidation reactor, and new reduction
>> reactor too. I also immersed the capillary line fully in liquid N2. I checked
>> for leaks, and also injected air in the system (5 to 10uL), and every time I
>> did so I could get nice N2 peaks, of about 12V for mass
>> So far so good, I thought. Then I injected Ethyl Acetate. Almost every time I
>> did that, the background for masses 28 and 29 would increase from nearly
>> 100mV at the beginning to around 2000mV at about 600s, and stay there
>> permanently, even if I change the backflush. The only way that I managed to
>> decrease the background again was to remove the line from the liquid N2 bath.
>> I repeated the procedure several times and it was always the same: good N2
>> peaks for air, strange increase in background for Ethyl Acetate. In addition,
>> when the background increases the way I said, I get no more peaks for air,
>> unless I take out the line from liquid N2 and try again.
>> One more thing that I tried was to inject ethyl acetate without the liquid
>> N2, and check for mass 44. I got a huge peak (>50V) followed by a decrease in
background again, with time.
>> In summary, I think someway CO2 (or H2O?) is blocking the line in the liquid
>> N2 trap, and at the same time air gets inside (so the increase in the
>> background) from somewhere (I have some connections through the capillary
>> I appreciate any help.
>> Matheus C. Carvalho
>> Senior Research Associate
>> Centre for Coastal Biogeochemistry
>> Southern Cross University
>> Lismore - Australia
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