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A Higher Initial GC Oven Temperature Can Cause DDT Degradation – Is There Anything That Does Not Cause DDT Degradation, Jack?

12 Sep 2011

In recent blogs I’ve relayed a litany of things that can cause DDT degradation when analyzing samples via GC-ECD as part of EPA Method 8081b for organochlorine pesticides, but have you considered that the GC initial oven temperature might also play a role?  (OK, this guy has finally gone off the deep end, because there is no way that can make a difference.)  Well, yes, I may be Common Loony, but I have the data to prove it below.  It happens when you’re using an Agilent GC and you don’t have wool in the liner and you make that ultra fast injection with the Agilent 7683 autosampler and you have a higher initial oven temperature. 

Notice in the figure below that DDT breakdown percentage goes from about 5 up to about 9 just by increasing the oven temperature start from 40°C to 120°C.  That’s because with the Agilent splitless inlet design, the bottom of the liner, and more importantly, the metal inlet seal, reside inside the GC oven.  A hotter oven means a hotter seal means more DDT breakdown if you are NOT using wool in the liner to stop the injected sample.

I show two photographs below that are significant to the work.  Taken from inside the Agilent 6890 GC oven, one is the split/splitless inlet with the nut warmer cup in its proper place (some of you are thinking that the proper place for that #$%^ thing is in the trash can, I know).  The other photo shows the inlet without the nut warmer cup.  I USED the nut warmer cup for my experiments here.  (If you look really closely you can see that the bottom of the inlet is actually cooler when the nut warmer cup is absent and the initial oven is relatively cool.) 

OK, I was just kidding about looking really close at that photo to get a reading on the inlet temperature.  But wouldn’t it be great if you could do that?  No more burned fingers!

Check out the bad juju that goes down when not using the nut warmer cup.


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