Kirkels F M S A, Cerli C, Federherr E, Gao J, Kalbitz K
University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics, Earth Surface Science, Science Park 904, 1098 XH, Amsterdam, The Netherlands.
Rapid Commun Mass Spectrom. 2014 Dec 15;28(23):2574-86. doi: 10.1002/rcm.7053.
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.
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.
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 ‰).
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.
溶解有机碳（DOC）在碳循环中起着重要作用，因此非常需要精确且常规地测量δ(13)C值和DOC浓度。为此已开发出一种有前景的新系统。然而，这项新技术的广泛应用需要对分析性能进行深入评估，本文对此进行了描述。
将高温燃烧总有机碳分析仪与连续流同位素比率质谱仪（TOC/IRMS）联用，用于同时分析总DOC浓度和δ(13)C特征。对分析性能（精密度、记忆效应、线性、体积/浓度效应、准确度）进行了全面评估，包括低DOC浓度和天然DOC等实际且具有挑战性的条件。
对于多种DOC溶液的δ(13)C分析，实现了高精度（标准偏差，SD主要≤0.1‰）和高准确度（R(2)=0.9997）。同时，DOC浓度测量也取得了良好结果。对天然丰度和轻度(13)C富集的DOC、广泛的浓度范围（约0.2 - 150 mgC/L）和进样体积（0.05 - 3 mL）的评估表明，记忆效应轻微/可忽略不计，线性良好且使用灵活。最后，TOC/IRMS成功应用于测定低DOC浓度（<2 mgC/L）以及来自不同陆地、淡水和海洋环境的DOC（SD≤0.23‰）。
TOC/IRMS能够快速可靠地测量水样中的DOC浓度和δ(13)C值，无需预浓缩和冷冻干燥。进一步的研究应聚焦于复杂的含盐基质和极低的DOC浓度，以实现潜在的0.2 mgC/L下限。因此，TOC/IRMS将通过高分辨率的常规δ(13)C分析，极大地推动陆地和水生环境中的DOC研究。
