Feasibility Study on Quantitative Analysis of Sulfide Concentration and pH of Marine Sediment Pore Water via Raman Spectroscopy
TIAN Zhi-xian1, 3, ZHANG Xin1*, LIU Chang-ling2, MENG Qing-guo2, YAN Jun1
1. Institute of Oceanology，Chinese Academy of Sciences，Qingdao 266071，China 2. Key Laboratory of Gas Hydrate，Ministry of Land and Resources，Qingdao Institute of Marine Geology，Qingdao 266071，China 3. University of Chinese Academy of Sciences，Beijing 100049，China
Abstract：Marine sediment pore water is one of the important objects in the study of global environmental change, marine geology and biogeochemistry. Anoxic pore waterin highly reducing deep-sea sediments commonly contains a large amount of dissolved sulfide (H2S and HS-). The sulfide species within sediment pore water are significant not only because the importance of themselves, but also because they exist as a function of pH which is another key parameter in pore water study. As degassing and chemical equilibrium altering are both inevitable, concentrations of sulfide species and pH value of marine sediment pore water acquired with traditional non-in situ technologies are of great uncertainty, and cannot represent the real geochemistry information. However, the recent deployment of an in situ laser Raman pore water sampler allows us to observe spectral sulfide signals of marine sediments in situ and in real time, which provide us a new technique to solve this problem. Sulfide species in water have a relatively strong Raman signal, which often appears in the form of a characteristic overlapping peak between 2 550~2 620 cm-1 and can be decomposed into HS- at 2 572 cm-1 and H2S at 2 592 cm-1. In the present paper, quantitative analysis ofH2S and HS- with Raman spectroscopy is proved practicableand the accuracy is good. The pH of pore water is an important influencing factor of the diagenetic processes. As H2S and HS- are conjugate acid-base pairs, sulfide specieswithin pore water exist as a function of pH and their concentration ratio depend on pH. This relationship is also shown in the Raman spectrum. To formulate thepore water pH calculation, sulfide solutions with pH range from 6.11 to 13.05were prepared and their Raman spectra were observed. It is verified that the morphology of overlapping peaks change regularly with pH values. This phenomenon provides us the possibility of measuring the pH of pore water in situ via Raman spectroscopy. Based on peaks decomposition and correlativity analysis, we proposehere a novel in situ pH measuring method for sediment pore water containing sulfide. This method can be used to measure the pH of pore water when the overlapping peak of sulfide is resolvable. The application scope of this pH measuring method in this study is 6.11~8.32, which covers almost all pH value of marine sediment pore water already known. The study provides additional technical reference for obtaining high-fidelity information of marine sediment pore water.
田陟贤1,3，张 鑫1*，刘昌岭2，孟庆国2，阎 军1 . 海洋沉积物孔隙水硫化物浓度与pH值的拉曼定量分析可行性实验研究 [J]. 光谱学与光谱分析, 2015, 35(03): 649-656.
TIAN Zhi-xian1, 3, ZHANG Xin1*, LIU Chang-ling2, MENG Qing-guo2, YAN Jun1 . Feasibility Study on Quantitative Analysis of Sulfide Concentration and pH of Marine Sediment Pore Water via Raman Spectroscopy. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2015, 35(03): 649-656.
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