2. A novel single-run dual temperature combustion (SRDTC) method for the determination of organic, inorganic and total carbon Isabella Bisutti, Ines Hilke, Jens Schumacher and Michael Raessler Max-Planck-Institut für Biogeochemie, Hans-Knoell-Strasse 10, D-07745 Jena, Germany

3. Target: exact determination of inorganic and organic carbon in soil samples for evaluation of the carbon cycles on regional and global scales soils contain 2200 Pg (10 15 g) carbon in the first 100 cm 2/3 OC and 1/3 IC soils contain three times more carbon than above- ground biomass

4. Classical methods for determination of OC and IC: combustion of sample to determine total carbon (TC) either acid or ashing pretreatment removes IC or OC remaining form of carbon is determined by combustion complementary part of carbon is calculated by difference ACID PRETREATMENT (ISO 10694) 1 st combustion: TC 2 nd combustion: OC IC = TC - OC

5. Disadvantages (1) acid pretreatment: non-quantitative removal of carbonate carbon great variability of results possible loss of soluble OC possible loss of volatile organic carbon (VOC)

6. Disadvantages (2) ashing pretreatment: thermal instability of carbonates uncertainty of complete OC removal neither acid nor ashing pretreatment provide information on TC, OC and IC in ONE single analitycal run

7. Carbonate minerals in soil samples

8. Possible solution dry combustion at TWO DIFFERENT temperatures OC is combusted at lower T while higher T are needed for complete decomposition of IC Disadvantage samples have to be analyzed twice equilibration of furnace longer analyses times possible loss of VOC not detected

9. Suggested Solution: SRDTC instrumental device: Liqui TOC, Elementar GmbH dynamic heater with catalytic post-combustion TC,OC and IC from ONE sample with ONE analysis no loss of VOC; all carbon is oxidized indication of thermally instable carbonates

12. Selection of combustion temperatures

14. Synthetic mixtures and mixing ratios Mixture: Magnesite-Cellulose in sand Magnesite-Wood in sand Calcite-Cellulose in sand Calcite-Wood in sand Calcite-Cellulose in sand-bentonite Calcite-Wood in sand-bentonite Ratio OC:IC in [%] 0.25 - 0.001 0.25 - 1.00 0.25 - 10.00 2.5 - 1.00 2.5 - 10.00 5.00 - 0.1 5.00 - 1.00 5.00 - 10.00

15. Combustion of Lignine and Calcite

16. Recovery of SRDTC analyses of synthetic mixtures (N=216) OC 107 ± 23.1 % IC 100 ± 16.9% TC 104 ± 6.7%

17. Expected OC vs.OC by SRDTC

18. SRDTC vs. ISO 10694

19. Acknowledgements Ralf Dunsbach, Klaus-Peter Sieper Elementar Analysensystem GmbH, Hanau, Germany Birgit Kreher-Hartmann, Mineralogische Sammlung, University of Jena Kristin Lober, Michael Rothe, Willi Brand, MPI Biogeochemie, Jena