Quantitative Determination of Sulfate in Hydrate and Water Systems by Raman Spectrometry
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摘要:
硫酸根含量是天然气水合物孔隙水中重要的参数之一，硫酸根与水合物的赋存关系已成为天然气水合物地球化学异常研究的重要组成部分。为了更深入地了解硫酸根浓度异常产生的原因和机制，建立一种实时、快速的测定方法就显得尤为重要。本文利用自行设计的天然气水合物反应装置，建立了海水中硫酸根在高压低温环境下的拉曼光谱定量测定方法。硫酸根的浓度（ρ）在2.0~70.0 g/L范围内，与其拉曼光谱参数（R）有良好的线性关系，线性回归方程为R=0.0013ρ-0.000066，相关系数r = 0.9998。方法检出限为0.2 g/L，精密度（RSD，n=12）为2.5%~3.4%，回收率为102.1%~123.8%。测试结果表明，采用拉曼光谱法可在线检测天然气水合物-水体系中硫酸根的浓度变化；相对于离子色谱法，具有不破坏原样品和方便快捷等优点。通过对硫酸根浓度变化的初步分析，发现其浓度呈阶梯状升高，认为天然气水合物的形成是一个气体溶解-成核-生长反复进行的过程，直至整个反应体系达到平衡。
Abstract: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.
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Key words:
- nature gas hydrate /
- sulfate /
- Raman spectrometry /
- on-line quantitative determination
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表 1 仪器工作条件
Table 1. Working parameters of the laser Raman spectrometry instrument
工作参数 设定条件 激光光源 532 nm 激光功率 80 mW 物镜 20倍 光栅刻线数 2400线/mm 拉曼位移范围 500~4000 cm-1 积分时间 1~10 s 
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表 2 方法精密度实验
Table 2. Precision tests of the method
K2SO4标准样品的浓度(g/L) K2SO4标准溶液测定浓度 RSD(%) 分次测定值 平均值 5.0 g/L 5.6 5.3 5.7 5.2 5.8 5.5 5.5 3.4 5.8 5.5 5.5 5.4 5.7 5.4 35.0 g/L 37.4 36.0 36.7 37.9 36.4 36.5 36.4 2.5 36.5 36.1 36.0 36.6 36.5 34.1
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表 3 方法回收率
Table 3. Recovery tests of the method
海水样品(50 ml) 加入量(g) 测定量(g) 回收量(g) 回收率(%) 平均回收率(%) RSD(%) 4.9 g/L 0.0500 0.3078 0.0613 122.6 123.8 23.6 0.2941 0.0476 95.1 0.3233 0.0768 153.6 0.1000 0.3521 0.1056 105.6 109.2 3.6 0.3552 0.1078 108.7 0.3599 0.1134 113.7 0.1500 0.3910 0.1445 96.3 102.1 5.7 0.3994 01529 101.9 0.4085 0.1620 108.0
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表 4 不同温度下K2SO4溶液浓度
Table 4. Solution concentration of K2SO4 in different temperatures
样品浓度(g/L) 温度(℃) 测定浓度(g/L) 相对误差(%) 5.0 2 5.1 1.9 5.0 5 5.1 2.3 5.0 10 5.1 1.0 5.0 15 5.0 -0.2 5.0 20 4.9 -1.3 5.0 25 4.9 -1.6
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表 5 不同压力下K2SO4溶液浓度
Table 5. Solution concentration of K2SO4 in different pressures
样品浓度(g/L) 压力(MPa) 测定浓度(g/L) 相对误差(%) 5.0 0 4.9 -1.2 5.0 2 5.0 0.9 5.0 4 5.1 1.0 5.0 6 5.0 -0.2 5.0 8 4.9 -1.3
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[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] doi: 10.1007/BF01204496
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