电感耦合等离子体发射光谱法测定地热水中的硫化物

地热水中的硫化物(H_2S、HS~-和S~(2-))通常受到硫酸根、亚硫酸根、硫代硫酸根等硫元素的共存干扰,并且硫化物具有热、光、氧不稳定性,在水样保存、前处理、标准溶液配制等环节影响着测试的准确度和精密度。本文在现场采集的地热水水样中加入乙酸锌及氢氧化钠,使硫化物形成硫化锌沉淀而与溶液分离,将此沉淀溶于双氧水和逆王水,使低价态的S2-氧化成稳定的SO_4~(2-),选择易于纯化且性质稳定的硫酸钠配制硫标准储备液,以182.624 nm谱线作为硫元素分析谱线,应用电感耦合等离子体发射光谱法测定出地热水样中的硫化物含量。硫的浓度在0.1~100 mg/L范围内与其发射强度呈线性(相关系数为0.9994);方法检出限为0.009 mg/L,相对标准偏差(n=11)低于1.80%,实际水样中硫化物的加标回收率介于99.0%~103.0%。与前人相关测试方法相比,本方法的技术指标具有优势。

Determination of Sulfide in Geothermal Water by Inductively Coupled Plasma-Optical Emission Spectrometry

The existing of sulfur-containing compounds, such as sulfate, sulfite and thiosulfate, could impact the determination of sulfide (H₂S, HS^- and S^2-) in geothermal water. In addition, the detection accuracy and precision would also be influenced by sample treatment process including sample collecting, sample pretreatment, standard solution preparation and so on. Therefore, it is of great importance to build a simple, accurate method for sulfide detection in water sample. Herein, a method containing following steps was built to pretreat samples and detect their sulfide concentration. Firstly, zinc acetate and sodium hydroxide were added to water sample collected in site, then sulfide would be precipitated as zinc sulfide and separated from water. Secondly, the precipitation would be dissolved in hydrogen peroxide and Lefort aqua regia in which S^2- would be oxidized to SO₄^2-. Thirdly, Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) was employed to detect sulfur content. Sample pretreatment, standard solution preparation method and analytical spectral line for sulfur were screened and optimized. It was found that S^2- concentration within the range of 0.1-100 mg/L was linearly associated with emission intensity. Detection limit of the method was 0.009 mg/L, relative standard deviation (n=11) was less than 1.80%, and adding standard recovery was between 99.0-103.0%. The results matched well with the data detected by iodometry.