A comparative study of methods for determining carbonate content in marine and terrestrial sediments
A comparative study of methods for determining carbonate content in marine and terrestrial sediments
复制标题
海洋和陆地沉积物中碳酸盐含量测定方法的比较研究
DOI：
10.1016/j.marpetgeo.2020.104337
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发表时间：
2020-06-01
影响因子：
4.2
通讯作者：
Shang, Fei
中科院分区：
文献类型：
--
作者：
Fu, Hanjing;Jian, Xing;Shang, Fei
碳酸盐可以在地球表面的各种环境中产生，例如浅海和深海、大陆湖泊、土壤和地下含水层。沉积物中碳酸盐含量是古海洋学和古气候学的重要指标，常被用来重建地球的古环境演化。据报道，有许多方法可用于测量沉积物中碳酸盐的含量，但这些方法的性能（如准确度和精确度、误差引起的因素、可操作性、成本和时间）仍有待研究。本文采用酸碱滴定法、气体定量法和基于燃烧的烧失量法（LOI）三种常用的非仪器方法，结合X射线衍射矿物相分析，对深海沉积物碳酸盐含量数据进行了比较（水深1218 ~ 6147 m）和青藏高原北方柴达木盆地新生代沉积岩。结果表明，大多数方法的数据精度与沉积物中的矿物组成（如碳酸盐种类和粘土矿物含量）和分析操作密切相关。非仪器方法通常表现出低精度（平均值）。测定低碳酸盐含量（<20%wt）沉积物的相对标准偏差为3.36%。在这三种方法中，LOI方法表现最好，具有相对较高的准确性（平均）。回收率为99.79%）和精密度（avg.当测定具有简单矿物成分（例如仅碳酸钙）的富碳酸盐沉积物时，RSD为0.27%）。尽管粘土矿物脱羟基可能影响测定结果，但LOI法具有操作简便、耗时短、便于批量测定等优点。酸碱滴定法和气体定量法显示中等精度（平均值）。精密度分别为108.64%和101.85%。此外，分析方法中的样品量、反应时间、温度、试剂浓度、称量误差、滴定终点判断等因素也会影响数据质量。该研究为碳酸盐岩测定方法的选择提供了重要的依据，对碳酸盐岩相关的地学研究具有一定的参考价值。
Carbonate can be produced in a variety of environments on the Earth's surface, such as shallow seas and deep oceans, continental lakes, soils and subsurface aquifers. The carbonate content of sediments is an important proxy in paleoceanography and paleoclimatology and is often used to reconstruct paleoenvironmental evolution of the earth. Many methods have been reported to measure the content of carbonate in sediments, but how those methods perform (e.g. degree of accuracy and precision, error-induced factors, operability, cost and time) remains understudied. Here, we employ three widely-used non-instrumental methods, including acid-base titration, gasometric method, and loss on ignition (LOI) based on muffle combustion, together with X-ray diffraction for mineral phase analysis, to compare the carbonate content data of sediments from deep ocean (water depths from 1218 m to 6147 m) of the western Pacific and Cenozoic sedimentary rocks from the Qaidam basin, northern Tibetan Plateau. The results show that data accuracies of most methods are closely related to mineral compositions in sediments (e.g. carbonate species and clay mineral contents) and analytical operations. Non-instrumental methods generally demonstrate low precisions (avg. RSD of 3.36%) in determining sediments with low carbonate contents ( < 20% wt). Among the three approaches, the LOI method performs best with relatively high accuracy (avg. recovery of 99.79%) and precision (avg. RSD of 0.27%) when determining carbonate-rich sediments with simple mineral compositions (e.g. only calcium carbonate). Although dehydroxylation of clay minerals might influence the results, the LOI method has advantages of ease of operation, short time-consuming and convenience for batch determinations. Acid-base titration and gasometric methods indicate moderate precisions (avg. RSD of 1.73% and 2.76%, respectively) and accuracies (108.64% and 101.85%, respectively) with quick measurement, affordable cost and requirement of high-quality manual operation. Additionally, we suggest that the analytical procedures, such as sample size, reaction time, temperature, reagent concentration, weighing error, endpoint judgement of titration can influence the data quality. This study provides significant selecting principles for carbonate determination methods and would be beneficial to carbonate-related study in various aspects of geosciences.