Federherr E, Cerli C, Kirkels F M S A, Kalbitz K, Kupka H J, Dunsbach R, Lange L, Schmidt T C
Instrumental Analytical Chemistry, University of Duisburg-Essen, Universitätsstr. 5, 45141, Essen, Germany; Research and Innovation, Elementar Analysensysteme GmbH, Donaustr. 7, 63452, Hanau, Germany.
Rapid Commun Mass Spectrom. 2014 Dec 15;28(23):2559-73. doi: 10.1002/rcm.7052.
Traditionally, dissolved organic carbon (DOC) stable isotope analysis (SIA) is performed using either offline sample preparation followed by elemental analyzer/isotope ratio mass spectrometry (EA/IRMS) or a wet chemical oxidation (WCO)-based device coupled to an isotope ratio mass spectrometer. The first method is time-consuming and laborious. The second involves the risks of underestimation of DOC concentration and isotopic fractionation due to incomplete oxidation. The development of an analytical method for accurate and sensitive DOC SIA is described in this study.
A high-temperature combustion (HTC) system improves upon traditional methods. A novel total organic carbon (TOC) system, specially designed for SIA, was coupled to an isotope ratio mass spectrometer. An integrated purge and trap technique (peak focusing), flexible injection volume (0.05-3 mL), favorable carrier gas flow, modified ash crucible, new design of combustion tube and optimized drying system were used to achieve the necessary performance.
The system can reliably measure concentrations up to 1000 mgC/L. Compounds resistant to oxidation, such as barbituric acid, melamine and humic acid, were analyzed with recovery rates of 100 ± 1% proving complete oxidation. In this initial testing, the δ(13) C values of these compounds were determined with precision and trueness of ≤ 0.2‰ even with 3.5% salinity. Further tests with samples with low DOC concentrations resulted in LOQSIA method values of 0.5 mgC/L and 0.2 mgC/L for LOQSIA instr , considering an accuracy of ± 0.5‰ as acceptable.
The novel HTC system coupled to an isotope ratio mass spectrometer resulted in significantly improved sensitivity. The system is suitable for salt-containing liquids and compounds that are resistant to oxidation, and it offers a large concentration range. A second paper (which follows this one in this issue) will present a more comprehensive assessment of the analytical performance with a broad set of solutions and real samples. This highly efficient TOC stable isotopic analyzer will probably open up new possibilities in biogeochemical carbon cycle research.
传统上，溶解有机碳（DOC）稳定同位素分析（SIA）是通过离线样品制备后接元素分析仪/同位素比率质谱仪（EA/IRMS）或基于湿化学氧化（WCO）的设备与同位素比率质谱仪联用进行的。第一种方法耗时费力。第二种方法存在由于氧化不完全导致DOC浓度低估和同位素分馏的风险。本研究描述了一种用于准确且灵敏的DOC SIA分析方法的开发。
高温燃烧（HTC）系统改进了传统方法。一种专门为SIA设计的新型总有机碳（TOC）系统与同位素比率质谱仪联用。采用集成吹扫捕集技术（峰聚焦）、灵活的进样体积（0.05 - 3 mL）、合适的载气流速、改进的灰化坩埚、燃烧管的新设计和优化的干燥系统来实现所需性能。
该系统能够可靠地测量高达1000 mgC/L的浓度。对氧化抗性化合物，如巴比妥酸、三聚氰胺和腐殖酸进行了分析，回收率为100 ± 1%，证明氧化完全。在此次初步测试中，即使盐度为3.5%，这些化合物的δ(13)C值的测定精度和准确性也≤ 0.2‰。对低DOC浓度样品的进一步测试得出，考虑到± 0.5‰的准确度可接受，LOQSIA方法值对于LOQSIA仪器为0.5 mgC/L和0.2 mgC/L。
与同位素比率质谱仪联用的新型HTC系统显著提高了灵敏度。该系统适用于含盐水溶液和抗氧化化合物，并且提供了较大的浓度范围。第二篇论文（本期紧随本文之后）将用一系列广泛的溶液和实际样品对分析性能进行更全面的评估。这种高效的TOC稳定同位素分析仪可能会为生物地球化学碳循环研究开辟新的可能性。
