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

RATIONALE 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. Copyright © 2014 John Wiley & Sons, Ltd.