School of Geography and Earth Sciences, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4K1.
Rapid Commun Mass Spectrom. 2012 Sep 15;26(17):2083-92. doi: 10.1002/rcm.6323.
Stable isotope compositions of natural waters, such as seawater, glaciers and basinal brines, can provide valuable information about Earth's hydrological cycle and its evolutionary history. However, a high concentration of dissolved ions in some natural waters hinders an accurate analysis of their oxygen isotope composition. A laboratory study was carried out in order to provide guidelines on how to resolve this analytical difficulty.
CO(2) gas was equilibrated with saline aqueous solutions of various chemical compositions at 25 °C. Subsequently, the oxygen isotope composition of the CO(2) was determined at different equilibration times using a dual-inlet isotope ratio mass spectrometer in order to evaluate the oxygen isotope salt effect and the rate of oxygen isotope exchange between CO(2) and the saline solution.
Using the experimentally determined oxygen isotope salt effects of aqueous chloride and sulfate solutions, an empirical method for the prediction of the oxygen isotope salt effect of a 1.0 molal chloride or sulfate solution was proposed. The rates of oxygen isotope exchange between CO(2) and saline solutions were also examined. Our experimental data indicates that the sequence of the oxygen isotope exchange time is as: MgSO(4) > CaCl(2) ≈ Na(2)SO(4) > NaCl > MgCl(2) > KCl > H(2)O.
The isotope salt effect and the kinetics of isotope exchange must be taken into account when the oxygen isotope composition of a saline aqueous solution is determined using the CO(2)-H(2)O equilibration method. Our experimental data and the proposed prediction method provide essential guidelines for the accurate δ(18)O analysis of saline aqueous solutions.
海水、冰川和盆地卤水等天然水的稳定同位素组成可以提供有关地球水文学循环及其演化历史的有价值信息。然而，一些天然水中溶解离子的高浓度阻碍了对其氧同位素组成的准确分析。进行了一项实验室研究，以便为如何解决这一分析难题提供指导。
将 CO(2)气体与具有不同化学成分的盐溶液在 25°C 下达到平衡。随后，在不同的平衡时间使用双入口同位素比质谱仪测定 CO(2)的氧同位素组成，以评估氧同位素盐效应和 CO(2)与盐溶液之间氧同位素交换的速率。
利用实验测定的水合氯化物和硫酸盐溶液的氧同位素盐效应，提出了一种预测 1.0 摩尔氯化物或硫酸盐溶液氧同位素盐效应的经验方法。还检查了 CO(2)和盐溶液之间的氧同位素交换速率。我们的实验数据表明，氧同位素交换时间的顺序为：MgSO(4) > CaCl(2) ≈ Na(2)SO(4) > NaCl > MgCl(2) > KCl > H(2)O。
在使用 CO(2)-H(2)O 平衡法测定盐溶液的氧同位素组成时，必须考虑同位素盐效应和同位素交换动力学。我们的实验数据和提出的预测方法为准确分析盐溶液的 δ(18)O 提供了必要的指导。
