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海洋沉积物孔隙水是研究海洋环境、地质与生物地球化学等问题的重要信息载体。高度还原的缺氧孔隙水普遍含有大量的溶解态硫化物(H_2S和HS)。这些硫化物既是孔隙水调查的重要研究对象也关系到另一重要地化参数-pH值。成分逸散、化学平衡破坏使传统非原位分析方法测定的海洋沉积物孔隙水硫化物浓度和pH值具有不确定性,难以反映原位地化信息。深海原位激光拉曼技术为解决这一问题提供了新的手段。孔隙水硫化物在拉曼光谱曲线上表现为位于2 550~2 620 cm~(-1)的明显拉曼重叠峰,包括H_2S的HS伸缩峰(2 592 cm~(-1))和HS~-的H-S伸缩峰(2 572 cm~(-1))。本研究在实验室条件下(25℃,0.1 MPa)对基于内标定法的H_2S与HS~-拉曼光谱定量分析进行了可行性研究,证实该技术可行且精度良好。H_2S与HS~-作为一组共轭酸碱对,其浓度比与pH值呈函数关系。通过配制不同pH值的含硫化物溶液并进行拉曼光谱分析,发现这一关系在拉曼光谱上表现为特征拉曼重叠峰形态和H_2S,HS~-分峰强度的规律性变化,即硫化物拉曼光谱参数与溶液pH值之间存在一定的耦合关系。基于谱峰分解和相关分析,提出了一种全新的含硫化物孔隙水pH原位测定方法。可测定硫化物拉曼重叠峰可分辨情况下的孔隙水pH,在本研究中为6.11~8.32,涵盖了已知的绝大多数孔隙水pH值范围。该研究为获取海洋沉积物孔隙水的高保真数据提供了新的技术参考。
Pore water in marine sediments is an important information carrier for the study of marine environment, geology and biogeochemistry. Highly reduced anoxic pore water generally contains large amounts of dissolved sulfur (H 2 S and HS). These sulfides are both important research objects for pore water investigations and relate to another important geochemical parameter, the pH value. The composition is volatile and chemical equilibrium disruption makes the sediment pore water sulfide concentration and pH value determined by the traditional non-in-situ analytical methods have uncertainties and it is difficult to reflect the in situ information. Deep-sea laser Raman technology provides a new solution to this problem. In the Raman spectrum, the sulfide of pore water showed obvious Raman overlapping peaks at 2 550 ~ 2 620 cm -1, including HS stretching peak (2 592 cm -1) of H 2 S and HS ~ - of the HS stretching peak (2 572 cm -1)). In this study, the feasibility of quantitative analysis of H 2 S and HS ~ - Raman spectra based on internal standardization was studied under laboratory conditions (25 ℃, 0.1 MPa). The results show that this technique is feasible and accurate. H 2 S and HS ~ - as a group of conjugate acid-base pairs, the concentration ratio as a function of pH. Through the preparation of sulfide solution with different pH value and Raman spectrum analysis, it was found that Raman spectrum showed a regular Raman spectrum and a regular change of peak intensities of H 2 S and HS ~ - There is a certain coupling relationship between Raman spectrum parameters and solution pH. Based on the spectral peak decomposition and correlation analysis, a new method for in situ pH measurement of sulfide-containing pore water was proposed. The pH of the pore water under which the overlapping peaks of the sulfide Raman can be resolved can be determined, which is 6.11 to 8.32 in the present study and covers most of the pore water pH range known. This study provides a new technical reference for obtaining high fidelity data of pore water in marine sediments.