title: A novel high-temperature combustion based system for stable isotope analysis of dissolved organic carbon in aqueous samples. II: optimization and assessment of analytical performance.
abstract: BACKGROUND
  Dissolved organic carbon (DOC) plays an important role in carbon cycling, making precise and routine measurement of δ(13)C values and DOC concentration highly desirable. A new promising system has been developed for this purpose. However, broad-scale application of this new technique requires an in-depth assessment of analytical performance, and this is described here.
  
  
  METHODS
  A high-temperature combustion Total Organic Carbon analyzer was interfaced with continuous flow isotope ratio mass spectrometry (TOC/IRMS) for the simultaneous analysis of the bulk DOC concentration and δ(13)C signature. The analytical performance (precision, memory effects, linearity, volume/concentration effects, accuracy) was thoroughly evaluated, including realistic and challenging conditions such as low DOC concentrations and natural DOC.
  
  
  RESULTS
  High precision (standard deviation, SD predominantly ≤ 0.15 ‰) and accuracy (R(2) = 0.9997) were achieved for the δ(13)C analysis of a broad diversity of DOC solutions. Simultaneously, good results were obtained for the measurement of DOC concentration. Assessment of natural abundance and slightly (13)C-enriched DOC, a wide range of concentrations (~0.2-150 mgC/L) and injection volumes (0.05-3 mL), demonstrated minor/negligible memory effects, good linearity and flexible usage. Finally, TOC/IRMS was successfully applied to determine low DOC concentrations (<2 mgC/L) and DOC from diverse terrestrial, freshwater and marine environments (SD ≤ 0.23 ‰).
  
  
  CONCLUSIONS
  TOC/IRMS enables fast and reliable measurement of DOC concentrations and δ(13)C values in aqueous samples, without pre-concentration and freeze-drying. Further investigations should focus on complex, saline matrices and very low DOC concentrations, to achieve a potential lower limit of 0.2 mgC/L. Thus, TOC/IRMS will give DOC research in terrestrial and aquatic environments a huge impulse with high-resolution, routine δ(13)C analysis.
authors.affiliation: University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics, Earth Surface Science, Science Park 904, 1098 XH, Amsterdam, The Netherlands.
authors.forename: F M S A
authors.initials: FM
authors.lastname: Kirkels
authors.forename: C
authors.initials: C
authors.lastname: Cerli
authors.forename: E
authors.initials: E
authors.lastname: Federherr
authors.forename: J
authors.initials: J
authors.lastname: Gao
authors.forename: K
authors.initials: K
authors.lastname: Kalbitz
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis*; D005618:Fresh Water / Q000737:chemistry*; D006358:Hot Temperature; D057230:Limit of Detection; D016014:Linear Models; D013058:Mass Spectrometry / Q000379:methods*; D010936:Plant Extracts / Q000737:chemistry; D015203:Reproducibility of Results; D012987:Soil / Q000737:chemistry*
chemical_list: D002247:Carbon Isotopes; D010936:Plant Extracts; D012987:Soil