Precise determination of equilibrium sulfur isotope effects during volatilization and deprotonation of dissolved H2S
Precise determination of equilibrium sulfur isotope effects during volatilization and deprotonation of dissolved H2S
复制标题
精确测定溶解 H2S 挥发和去质子化过程中的平衡硫同位素效应
DOI：
10.1016/j.gca.2019.01.016
复制
发表时间：
2019
影响因子：
5
通讯作者：
Adkins, Jess F.
中科院分区：
文献类型：
--
作者：
Sim, Min Sub;Sessions, Alex L.;Orphan, Victoria J.;Adkins, Jess F.
由于微生物硫酸盐还原作用，硫化物（H2S、HS− 和 S2−）在海洋孔隙水中普遍存在，构成生物地球化学硫循环的还原端。稳定同位素已被广泛用于限制硫循环，因为硫化合物的氧化还原转化（例如微生物硫酸盐还原）通常表现出相当大的动力学同位素效应。与硫酸根离子 (SO42−)（海水中最丰富的溶解硫形式）相比，H2S 具有挥发性，并且在接近中性 pH 值时也会去质子化。因此，硫化物物质之间的平衡同位素分配可以与涉及硫化物作为反应物或中间体的反应期间的动力学同位素效应重叠。先前测量 H2S 和 HS− 之间平衡分馏的实验尝试取得了不同的结果，这可能是由于溶液的离子强度差异很大。在本研究中，我们测量了 20.6±0.5°C、pH 值 2 至 8 范围内总溶解硫化物和气态 H2S 之间的硫同位素分馏，并计算了与溶解 H2S 去质子化相关的平衡同位素效应。通过使用Na2S的稀溶液，通过提高质谱技术的灵敏度，可以更好地控制由于离子强度而导致的H2S第一解离常数的不确定性。这反过来又使我们能够关闭实验中的硫同位素质量平衡，并提高估计分馏因子的准确性。平衡时，相对于气态 H2S 和 HS− 水溶液，H2S 水溶液中 34S 的富集量分别为 0.7‰ 和 3.1‰。含水 H2S 和 HS− 之间的估计分馏介于两个早期的实验报告之间，但在测量的不确定性范围内与最近的理论计算一致。
Sulfide (H2S, HS−, and S2−) is ubiquitous in marine porewaters as a result of microbial sulfate reduction, constituting the reductive end of the biogeochemical sulfur cycle. Stable isotopes have been widely used to constrain the sulfur cycle, because the redox transformations of sulfur compounds, such as microbial sulfate reduction, often exhibit sizable kinetic isotope effects. In contrast to sulfate ion (SO42−), the most abundant form of dissolved sulfur in seawater, H2S is volatile and also deprotonated at near neutral pH. Equilibrium isotope partitioning between sulfide species can therefore overlap with kinetic isotope effects during reactions involving sulfide as either reactant or intermediate. Previous experimental attempts to measure equilibrium fractionation between H2S and HS−have reached differing results, likely due to solutions of widely varying ionic strength. In this study, we measured the sulfur isotope fractionation between total dissolved sulfide and gaseous H2S at 20.6 ± 0.5 °C over the pH range from 2 to 8, and calculated the equilibrium isotope effects associated with deprotonation of dissolved H2S. By using dilute solutions of Na2S, made possible by the improved sensitivity of mass spectrometric techniques, uncertainty in the first dissociation constant of H2S due to ionic strength could be better controlled. This in turn allowed us to close sulfur isotope mass balance for our experiments and increase the accuracy of the estimated fractionation factor. At equilibrium, aqueous H2S was enriched in34S by 0.7‰ and 3.1‰ relative to gaseous H2S and aqueous HS−, respectively. The estimated fractionation between aqueous H2S and HS−lies between two earlier experimental reports, but agrees within the uncertainty of the measurements with a recent theoretical calculation.
登录
查看更多内容
影响因子：
6.1
作者：
Jans, U;Miah, MH
通讯作者：
Miah, MH
影响因子：
5
作者：
Migdisov, AA;Williams-Jones, AE;Alekhin, YV
通讯作者：
Alekhin, YV
DOI：
10.1061/(asce)0733-9372(2005)131:12(1676
发表时间：
2005-12
影响因子：
2.2
作者：
C. Yongsiri;J. Vollertsen;T. Hvitved‐Jacobsen
通讯作者：
C. Yongsiri;J. Vollertsen;T. Hvitved‐Jacobsen
与 HS- 质子化和 H2S 挥发相关的硫同位素效应。
DOI：
10.1016/0168-9622(86)90014-x
发表时间：
1986
期刊：
Isotope geoscience
影响因子：
--
作者：
B. Fry;H. Gest;J. Hayes
通讯作者：
J. Hayes
H2S 第二解离常数的近似值
影响因子：
5
作者：
M. Schoonen;H. Barnes
通讯作者：
H. Barnes