I did not have absolutly the same experience (enriched samples). Try next:
1. Check that your reduction column has pure copper, water trap is not
exhausted and oxygen from tank does not contain any nitrogen.
2. Put your capsules into each second cell of the autosampler. On my
experience the pulse of oxygen (when EA runs blank cell) helps to push out any
traces after the previous sample.
>===== Original Message From Stable Isotope Geochemistry
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>right now I am measuring enriched samples (up to 2 atom % 15N) on my NC2500
>with Delta Plus. I have a blank of about 10 mV and I noticed that my blank
>is also getting enriched during a run, up to a few hundred permil. The
>first blanks at the start of a run have normal values. When I check the
>source of the blank is comes mostly from the autosampler ( by moving the
>autosampler without tin cup and with O2 injection off).
>Allthough blank corrections are minor, I am a bit surprised that my blank
>is getting enriched.
>Does anyone have the same experience?
>Richard van Logtestijn
Sergey OLEYNIK, PhD
Ecology and Evolution
Dept. Biological Sciences
University of Illinois, Chicago
845 W. Taylor st.
UIC, 3342 SES
Chicago, IL 60607
Phone: office 312-9964584
lab 312-3550600 (voice)
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