不同方法萃取的溶解无机碳的δ13C值比较分析

孙海龙; 刘再华; 晏浩; 杨睿; 曾成; 王海静

不同方法萃取的溶解无机碳的δ13C值比较分析

中国科学院地球化学研究所/环境地球化学国家重点实验室

基金项目: 中科院“百人计划”项目、国家自然科学基金项目(40872168、41172232)

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出版历程
- 收稿日期: 2012-12-14
- 刊出日期: 2013-03-25

Comparison to the δ13C value in dissolved inorganic carbons extracted with different methods

Institute of Geochemistry / State Key Laboratory of Environmental Geochemistry, CAS

摘要

摘要: 为了测定水中溶解无机碳的δ13C值,通常可以利用两种方法对水中的DIC进行萃取:沉淀法和脱气法。但是,一直以来未有研究对这两种方法萃取同一水样DIC的δ13C值之间的差异进行对比分析,尤其是对于具有高CO2分压(pCO2)的水样。本文对两组分别代表深部岩溶系统(高pCO2)和表层岩溶系统(低pCO2)的水样分别同时利用这两种萃取方法萃取其DIC然后测定δ13CDIC值。对比发现利用脱气法萃取物测定得到的δ13CDIC值要显著高于利用沉淀法萃取物测定得到的δ13CDIC值。这是因为在脱气法萃取DIC的过程中,由于水的pCO2高于大气的pCO2,水中富含12C的CO2通过扩散作用逃逸到大气中,从而使δ13CDIC值偏正。这表明利用沉淀法萃取物测定的δ13CDIC值的精度要高于脱气萃取法的精度。对两种DIC萃取方法萃取物测定的δ13CDIC值之间的差与水样和大气之间的CO2分压差进行分析后发现,两者之间具有较好的正相关关系。由于深部岩溶系统的水样具有很高的pCO2,富含12C的CO2向大气逸出的量相对较多,从而导致相应的深部岩溶系统线性关系的斜率和截距均比表层岩溶系统的线性关系的斜率和截距为大。文中所建立的这些线性关系为校正脱气法萃取物测定得到的δ13CDIC值提供了一个可能的经验校正公式。
- 溶解无机碳 /
- 碳稳定同位素 /
- 沉淀法 /
- 脱气法 /
- 差异 /
- CO2分压 /
- 校正
Abstract: To obtain the δ13C values in dissolved inorganic carbon (DIC), the DIC is usually extracted from the water by the direct precipitation method or the gas evolution method. However, what is the difference between those measured δ13C values in DIC extracted with the two different methods, especially for the water samples with high CO2 partial pressure (pCO2)? Two groups of water samples representing endogenic karst system (with high pCO2) and epigenic karst system (with low pCO2) respectively are measured by the two methods. It is found that all of the measured δ13C values of DIC by the gas evolution method are higher than those by the direct precipitation method. This is resulted from the diffusive escape of CO2 from the water to the atmosphere when transferring the water to the glass vials in the laboratory because of the higher water pCO2 than that of the atmosphere. The finding demonstrates that the precision of the measured δ13C values by the direct precipitation method for DIC extraction is better than the gas evolution one. There is a linear positive correlation between the difference of the measured δ13C values of DIC by the two methods and the CO2 partial pressure difference between the water and the atmosphere. However, the linear correlation of the endogenic karst system is different with that of the epigenic karst system, the former having a higher constant term which is related to the increase of δ13C values of DIC caused by the de glassing of CO2 with low δ13C from vials. The linear correlations established here provide a possible calibration method for the measured δ13C values by using the gas evolution method, especially for the water samples taken from the endogenic karst system with high pCO2.
- dissolved inorganic carbon /
- stable carbon isotope /
- direct precipitation method /
- gas evolution method /
- difference /
- CO2 partial pressure /
- calibration

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