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Investigation of two novel approaches for detection of sulfate ion and methane dissolved in sediment pore water using Raman spectroscopy.

Du Z, Chen J, Ye W, Guo J, Zhang X, Zheng R - Sensors (Basel) (2015)

Bottom Line: With the aid of LCOF, the Raman signal of SO42- is found to be enhanced over 10 times compared to that obtained by a conventional Raman setup.The enrichment process is also found to be effective in the investigation to the prepared sample of methane dissolved in water.All the obtained results suggest that the approach proposed in this paper has great potential to be developed as a sensor for SO42- and CH4 detection in pore water.

View Article: PubMed Central - PubMed

Affiliation: Optics and Optoelectronics Laboratory, Ocean University of China, Qingdao 266100, China. mofeng212@163.com.

ABSTRACT
The levels of dissolved sulfate and methane are crucial indicators in the geochemical analysis of pore water. Compositional analysis of pore water samples obtained from sea trials was conducted using Raman spectroscopy. It was found that the concentration of SO42- in pore water samples decreases as the depth increases, while the expected Raman signal of methane has not been observed. A possible reason for this is that the methane escaped after sampling and the remaining concentration of methane is too low to be detected. To find more effective ways to analyze the composition of pore water, two novel approaches are proposed. One is based on Liquid Core Optical Fiber (LCOF) for detection of SO42-. The other one is an enrichment process for the detection of CH4. With the aid of LCOF, the Raman signal of SO42- is found to be enhanced over 10 times compared to that obtained by a conventional Raman setup. The enrichment process is also found to be effective in the investigation to the prepared sample of methane dissolved in water. By CCl4 extraction, methane at a concentration below 1.14 mmol/L has been detected by conventional Raman spectroscopy. All the obtained results suggest that the approach proposed in this paper has great potential to be developed as a sensor for SO42- and CH4 detection in pore water.

No MeSH data available.


Raman spectrum of CCl4 after extraction after conventional experimental setup.
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sensors-15-12377-f009: Raman spectrum of CCl4 after extraction after conventional experimental setup.

Mentions: As is known, the maximum concentration of dissolved methane is about 1.14 mmol/L (the concentration of its saturated solution under laboratory conditions), which is still too low to be detected by the LCOF-Raman (LWCC-3050) experimental setup. In order to detect the methane dissolved in water, an approach based on CCl4 extraction is introduced in this work. CCl4 is chosen as an extraction agent for two reasons: the solubility of CH4 in CCl4 is much larger than that in H2O and CCl4 is immiscible with water. Thus, the trace CH4 dissolved in water is enriched into CCl4 after the extraction. Then, the CCl4 after extraction is taken as samples for Raman spectrum acquisition. The molecular density of CH4 (C in Equation (1)) in CCl4 is much bigger than that in H2O. Finally, the Raman spectrum of CCl4 after the extraction acquired by the conventional experimental setup with an integration time of 0.1 s, which is an average result of ten measurements, is shown in Figure 9.


Investigation of two novel approaches for detection of sulfate ion and methane dissolved in sediment pore water using Raman spectroscopy.

Du Z, Chen J, Ye W, Guo J, Zhang X, Zheng R - Sensors (Basel) (2015)

Raman spectrum of CCl4 after extraction after conventional experimental setup.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4507585&req=5

sensors-15-12377-f009: Raman spectrum of CCl4 after extraction after conventional experimental setup.
Mentions: As is known, the maximum concentration of dissolved methane is about 1.14 mmol/L (the concentration of its saturated solution under laboratory conditions), which is still too low to be detected by the LCOF-Raman (LWCC-3050) experimental setup. In order to detect the methane dissolved in water, an approach based on CCl4 extraction is introduced in this work. CCl4 is chosen as an extraction agent for two reasons: the solubility of CH4 in CCl4 is much larger than that in H2O and CCl4 is immiscible with water. Thus, the trace CH4 dissolved in water is enriched into CCl4 after the extraction. Then, the CCl4 after extraction is taken as samples for Raman spectrum acquisition. The molecular density of CH4 (C in Equation (1)) in CCl4 is much bigger than that in H2O. Finally, the Raman spectrum of CCl4 after the extraction acquired by the conventional experimental setup with an integration time of 0.1 s, which is an average result of ten measurements, is shown in Figure 9.

Bottom Line: With the aid of LCOF, the Raman signal of SO42- is found to be enhanced over 10 times compared to that obtained by a conventional Raman setup.The enrichment process is also found to be effective in the investigation to the prepared sample of methane dissolved in water.All the obtained results suggest that the approach proposed in this paper has great potential to be developed as a sensor for SO42- and CH4 detection in pore water.

View Article: PubMed Central - PubMed

Affiliation: Optics and Optoelectronics Laboratory, Ocean University of China, Qingdao 266100, China. mofeng212@163.com.

ABSTRACT
The levels of dissolved sulfate and methane are crucial indicators in the geochemical analysis of pore water. Compositional analysis of pore water samples obtained from sea trials was conducted using Raman spectroscopy. It was found that the concentration of SO42- in pore water samples decreases as the depth increases, while the expected Raman signal of methane has not been observed. A possible reason for this is that the methane escaped after sampling and the remaining concentration of methane is too low to be detected. To find more effective ways to analyze the composition of pore water, two novel approaches are proposed. One is based on Liquid Core Optical Fiber (LCOF) for detection of SO42-. The other one is an enrichment process for the detection of CH4. With the aid of LCOF, the Raman signal of SO42- is found to be enhanced over 10 times compared to that obtained by a conventional Raman setup. The enrichment process is also found to be effective in the investigation to the prepared sample of methane dissolved in water. By CCl4 extraction, methane at a concentration below 1.14 mmol/L has been detected by conventional Raman spectroscopy. All the obtained results suggest that the approach proposed in this paper has great potential to be developed as a sensor for SO42- and CH4 detection in pore water.

No MeSH data available.