> The samples were pretreated to eliminate any inorganic carbonates.
Have you checked if all carbonate was removed?
Put some of your stuff (the "normal" and the "new life from") in a gasbench vial and add some acid and see if you get a signal. Not very sensitive I guess but may give an idea if it worked.
How did you remove the carbonate? You may check Lorraine et al.  or Brodie et al.  for different methods and effects.
 Lorrain et al. (2003). Decarbonation and preservation method for the analysis of organic C and N contents and stable isotope ratios of low- carbonated suspended particulate material. Analytica Chimica Acta, 491, 125–133.
 Brodie, Chris R., Leng, Melanie J., Casford, James S.L., Kendrick, Christopher P., Lloyd, Jeremy M., Yongqiang, Zong, Bird, Michael I., Evidence for bias in C and N concentrations and δ13C composition of terrestrial and aquatic organic materials due to pre-analysis acid preparation methods, Chemical Geology (2011), doi: 10.1016/j.chemgeo.2011.01.007
Dr. Robert van Geldern
GeoZentrum Nordbayern / Applied Geosciences
University of Erlangen-Nuremberg
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