Evaluation of δ13C and δ15N Uncertainties Associated with the Compound-Specific Isotope Analysis of Geoporphyrins
Evaluation of δ13C and δ15N Uncertainties Associated with the Compound-Specific Isotope Analysis of Geoporphyrins
复制标题
DOI：
10.1021/acs.analchem.9b04843
复制
发表时间：
2020-02-18
影响因子：
7.4
通讯作者：
Ohkouchi, Naohiko
中科院分区：
文献类型：
--
作者：
Isaji, Yuta;Ogawa, Nanako O.;Ohkouchi, Naohiko
地卟啉是光养生物所具有的氯色素的衍生物，其化合物特异性同位素分析提供了过去水生环境的地球化学循环的重要记录。在这里，我们评估了碳和氮同位素组成（Δ C-13和（Δ N-15）与高效液相色谱（HPLC）纯化和同位素测量的地卟啉的不确定性。对HPLC和我们的灵敏度改进的元素分析仪/同位素比质谱仪（nano-EA/IRMS）分析的总空白碳和氮的评价证实，空白碳可以校正，并且与同位素测量所需的地卟啉质量相比，空白氮可以忽略不计。虽然地卟啉表现出显著的峰内碳和氮同位素分馏，但在Ni-和VO-卟啉标准品的反相和正相HPLC分离期间没有观察到Δ C-13和Δ N-15值的系统性变化，Δ C-13和Δ N-15值的变化在+/-0.6份/千份和+/-1.2份/千份（2 σ）内，分别这些值与nano-EA/IRMS系统的仪器精密度相当（对于0.70 μ gC为+/-1.3/1000份，对于0.08 μ gN为+/-1.1/1000份，2 σ），证实了在反相和正相HPLC纯化过程中预计Δ C-13和Δ N-15值中没有实质性人为因素。我们的方法的灵敏度和精度，使我们能够确定Δ C-13和Δ N-15值的古代沉积物中发现的主要和次要的地卟啉，这将提供详细的信息光合初级生产者和碳和氮循环在过去。
Compound-specific isotope analyses of geoporphyrins, which are derivatives of chloropigments possessed by phototrophs, provide essential records of the biogeochemical cycle of past aquatic environments. Here, we evaluated uncertainties in carbon and nitrogen isotopic compositions (delta C-13 and (delta N-15) associated with high-performance liquid chromatography (HPLC) purification and isotopic measurements of geoporphyrins. Evaluation of total blank carbon and nitrogen for the HPLC and our sensitivity-improved elemental analyzer/isotope ratio mass spectrometer (nano-EA/IRMS) analysis confirmed that blank carbon can be corrected and that blank nitrogen is negligible compared to the mass of geoporphyrins required for the isotopic measurement. While geoporphyrins exhibited substantial in-peak carbon and nitrogen isotopic fractionations, no systematic changes in delta C-13 and delta N-15 values were observed during reversed- and normal-phase HPLC isolation of Ni- and VO-porphyrin standards, with the changes in delta C-13 and delta N-15 values being within +/- 0.6 parts per thousand and +/- 1.2 parts per thousand (2 sigma), respectively. These values are comparable to the instrumental precision of the nano-EA/IRMS system (+/- 1.3 parts per thousand for 0.70 mu gC and +/- 1.1 parts per thousand for 0.08 mu gN, 2 sigma), confirming that no substantial artifact in the delta C-13 and delta N-15 values would be expected during the reversed and normal-phase HPLC purification. The sensitivity and precision of our method enable us to determine delta C-13 and delta N-15 values of both major and minor geoporphyrins found in ancient sediments, which would provide detailed information on the photosynthetic primary producers and the carbon and nitrogen cycles in the past.