Impact of nitrate contamination on the analysis of carbon and oxygen isotopes in carbonate and a low‐temperature phosphoric acid digestion approach for online sample preparation
Impact of nitrate contamination on the analysis of carbon and oxygen isotopes in carbonate and a low‐temperature phosphoric acid digestion approach for online sample preparation
复制标题
硝酸盐污染对碳酸盐中碳和氧同位素分析的影响以及在线样品制备的低温磷酸消解方法
DOI：
10.1002/rcm.8289
复制
发表时间：
2019
影响因子：
2
通讯作者：
Yourong Tian
中科院分区：
文献类型：
--
作者：
Bin Hu;Jianfei Gao;Changfu Fan;Yanhe Li;Yan Qin;Yue Zhao;Yourong Tian
基本原理：高温磷酸消解-连续流同位素比值质谱法（CF-IRMS）是测定碳酸盐中碳氧同位素的标准方法之一。然而，常规纯化方案尚未通过具有硝酸盐污染的样品进行测试。在这里，我们表明，标准协议是无法测量这样的样品具有令人满意的准确度和精密度。研究方法：我们测试了低温（25°C）磷酸消化法结合CF-IRMS用于测量硝酸盐浓度约为1%的天然碳酸盐样品和硝酸盐掺杂碳酸盐标准品。我们还记录了从硝酸盐掺杂的碳酸盐标准品中提取的气体的拉曼光谱，以识别影响结果的气体种类。结果：在72°C下消化的硝酸盐掺杂碳酸盐标准品的δ 18 O值的准确度和精密度远低于常规测量。对于在25°C下反应的掺杂标准物的测量，δ 13 C和δ 18 O值的准确度和精密度与正常结果没有区别。拉曼光谱表明，高温消解产生的NO2可能是氧同位素测量的干扰物质。结论：低温消解是测量硝酸盐污染的碳酸盐样品中碳和氧同位素的可靠方法，因为可以大大减少NO2的形成。这种方法可以应用于一些富含硝酸盐的洞穴沉积物、碳酸盐岩和其他含有硝酸盐污染的样品。
Rationale: High‐temperature phosphoric acid digestion combined with continuousflow isotope ratio mass spectrometry (CF‐IRMS) is one of the standard methods for the determination of carbon and oxygen isotopes in carbonate. However, the routine purification protocol has not been tested by samples with nitrate contamination. Here we show that the standard protocol is not capable of measuring such samples with satisfactory accuracy and precision..Methods: We tested the low‐temperature (25°C) phosphoric acid digestion method combined with CF‐IRMS for the measurement of natural carbonate samples with ~1% nitrate concentration and nitrate‐doped carbonate standards. We also recorded the Raman spectra of the gases extracted from the nitrate‐doped carbonate standards to identify the gas species that affect the results..Results: The accuracy and precision of δ18O values for nitrate‐doped carbonate standards digested at 72°C are much poorer than routine measurements. For the measurements of doped standards reacted at 25°C, the accuracy and precision of the δ13C and δ18O values are indistinguishable from normal results. Raman spectra demonstrate that NO2 generated from high‐temperature digestion is the possible interference species for oxygen isotope measurement..Conclusions: Low‐temperature digestion is a reliable method for the measurement of carbon and oxygen isotopes in nitrate‐contaminated carbonate samples because the formation of NO2 can be largely reduced. This approach can be applied to some nitrate‐rich speleothems, evaporites and other samples with nitrate contamination.