Dissolved inorganic carbon (DIC) is one of the most important parameters to be measured in seawaters for climate change studies. Its quantitative assessment requires analytical methodologies with overall uncertainties around 0.05% RSD for clear evaluation of temporal trends. Herein, two alternative isotope dilution mass spectrometry (IDMS) methodologies (online and species-specific) using an isotope ratio mass spectrometer (IRMS) and two calculation procedures for each methodology have been compared. As a result, a new method for the determination of DIC in seawaters, based on species-specific IDMS with isotope pattern deconvolution calculation, was developed and validated. A ¹³C-enriched bicarbonate tracer was added to the sample and, after equilibration and acidification, the isotope abundances at CO₂ masses 44, 45, and 46 were measured on an IRMS instrument. Notably, early spiking allows correcting for evaporations and/or adsorptions during sample preparation and storage and could be carried out immediately after sampling. Full uncertainty budgets were calculated taking into account all the factors involved in the determination (initial weights, concentration and isotope abundances of standards, and final IRMS measurements). The average DIC value obtained for CRM seawater agreed very well with the certified value. Propagated precision obtained ranged from 0.035 to 0.050% RSD for individual sample triplicates. Reproducibility, assessed by three independent experiments carried out in different working days, was excellent as well (−0.01% and 0.057%, error and full combined uncertainty, respectively). Additionally, the approach proposed improves on established methods by simplicity, higher throughput (15 min per sample), and lower volume requirements (10 mL).

中文翻译：

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同位素稀释质谱法用于气候变化研究中高精度测定海水中溶解的无机碳

溶解无机碳（DIC）是海水中用于气候变化研究的最重要参数之一。其定量评估需要总体不确定性约为RSD 0.05％的分析方法，以便对时间趋势进行清晰的评估。本文中，比较了使用同位素比率质谱仪（IRMS）的两种替代同位素稀释质谱法（IDMS）方法（在线和特定物种）和每种方法的两种计算程序。结果，开发并验证了一种新的测定海水中DIC的方法，该方法基于具有同位素模式反褶积计算的特定物种IDMS。将富含¹³ C的碳酸氢根示踪剂添加到样品中，平衡和酸化后，CO处的同位素丰度_2个在IRMS仪器上测量质量44、45和46。值得注意的是，早期加标可以校正样品制备和存储过程中的蒸发和/或吸附，并且可以在采样后立即进行。考虑到确定中涉及的所有因素（初始权重，标准品的浓度和同位素丰度以及最终的IRMS测量），计算了完全不确定性预算。CRM海水获得的平均DIC值与认证值非常吻合。一式三份的样品获得的传播精度范围为RSD的0.035％至0.050％。通过在不同工作日内进行的三个独立实验评估的可重复性也非常好（分别为-0.01％和0.057％，误差和完全不确定性）。此外，