Ethyl acetaoacetate by CG

[Míriam]

Hi everyone!
I´m having some problems to analyze Ethyl acetoacetate by CG.The supplier of this solvent has sent me their analize method but it doesn´t work when I have tried.I am obtainig a peak with a big tail and bad resolution.The method of my supplier is the next:
HP-1 30m, 0,25mm,0.25µm T injector=180ºC Tdetector=250ºC
Flow=2 ml/min(hydrogen) split flow=200ml/min
T initial=50ºC(1.5 min) Rate=40ºC/min Tfinal=200ºC(4.0 min)
I only have to my disposal the next coloum:
HP-1 30m, 0,32mm,5µm and I have to work with Helium instead of Hidrogen due to the gas istalation only let work me with this gas.
Could be the poor resolution caused by these two factors?
Thanks

[Peter Apps]

I presume that you are injecting ethyl acetoacetate and that you want to determine impurities.

First step is inlet maintenance - new liner, new septum, check that there is no crud lying in the inlet body, change the gold seal if you have that kind of GC. While you are doing that check that the column is properly positioned in the inlet.

If that does not work cut 1 m off the inlet end of the column.

Do you get sharp peaks with other samples ?

Peter

[chromatographer1]

It is possible if the sample has picked up water from the air the chemical will form an enol. This will tend to tail and broaden the peak, especially if excessive temperatures are used,....Temperatures that might be needed to elute the chemical in a timely manner.

Not an easy chemical to analyze.

best wishes,

Rod

[krickos]

Hi

Another possibility is the injector temperature of 180°C which corresponds to the boiling point of Ethyl acetaoacetate, I am familiar with methyl acetoacetate analysis but not this one, someone stated elevated temperatures could be an issue but for normal split injection it is normally so that you need to set injector temperature above the bp of the analyte/solvent to get an adequate vapourization.

[WK]

Hi - ethyl acetoacetate breaks down readily in hot injectors - it is difficult to analyse - I use
injector temperature 165degC in wool filled 4mm id liner to prevent it breaking down to ethanol.
WK

[krickos]

Hi - ethyl acetoacetate breaks down readily in hot injectors - it is difficult to analyse - I use
injector temperature 165degC in wool filled 4mm id liner to prevent it breaking down to ethanol.
WK

Intresting to learn new stuff, how is the peak shape? Do you use normal split injection or pulsed split injection?

[chromatographer1]

Dilute it with a non-protonoic solvent like methyl formate, and use direct injection if possible with a fast flow rate and low injection temperature. On-column would be great idea.

best wishes,

Rod

[WK]

Hi Krickos,
I should have said that in the analysis I'm not interested in the ethyl acetoacetate.
Miriam - how are you getting on with this?
Regards
WK

[Míriam]

Hi everybody!
I´ve done some changes with te injection temperature.When I work with a Tªinj=180ºC I obtain 2 peaks overlaped(firts corresponds to 30% and the other to 70%).When I work a Tªinj=120º I obtain only a peak with a little tail where before I found the first peak.I´ve injected insolate methyl acetoacetat, which is one the impurities declarated for my provieder with a % of 1% and its retention time correspond to the first peak.I am working with this program of temperatures
T=80ºC t=13min
Rate=30ºC/min T=250ºC t=10 min
Both peaks appear RT=25 min, so teh Tª in this moment is 250ºC.
I´he tied to work with lower Tª but then I obtain worse peak shape and the resolution between the two peaks doesn´t increase.
Does anybody know what could have been happened?
Thank you very much for your colaboration, your coments have given a lo of information.

[WK]

Hi All,
I think I should clarify that the ethyl acetoacetate in my liners breaks
down (at injector temperature > 170degC) to a component which
co-elutes with ethanol on the 624 column I use !
Regards
WK

[Míriam]

Hi everybody!
Finally I´ve solved the problem. I´m using low temperatures as well as in injector Tº(160ºC) and in coloum(110ºC) to elute ethyl acetoacetate. Otherwise, using high tempaeratures the peak break in two or three peaks.
Thanks everyone for the information, it has been very usefull.