Quantitative Determination of Sulfate in Hydrate and Water Systems by Raman Spectrometry

Sulfate content is one of the important parameters in pore water of gas hydrate. The relationship between sulfate and gas hydrate has become an important method to study geochemical anomalies of gas hydrate. It is particularly important to establish a fast and real time method in order to determine and therefore understand the cause and mechanism of sulphate concentration anomalies. An explanation of a uniquely designed synthetic experiment for gas hydrate is described in this paper, which is a method for the quantitative determination of sulfate in seawater using Raman Spectrometry at high pressure and low temperature. The relationship between the sulfate content and its Raman spectrum parameters was in a good linear agreement within 2.0-70.0 g/L. The equation of linear regression is R = 0.0013ρ-0.000066. The related coefficient is r = 0.9998. The detection limit is 0.2 g/L. The recoveries are 102.1%-123.8% with precision of 2.5%-3.4% (RSD, n = 12). The test result shows that the changes of sulfate content in gas hydrate and water system on-line by Raman spectroscopy can be detected. Compared to ion chromatography, the original samples remain intact with this method, and it is convenient and rapid. By preliminary analysis of the changes of sulfate content, it was founded that sulfate content basically presented ladder form rise and determined that the formation of gas hydrate was a repeated process of gas dissolution, nucleation and growth until the entire reaction system reaches equilibrium.