湿消解-原子荧光法测定煤中硒和砷

煤中微量元素砷、硒的含量与环境安全和居民健康密切相关，快速准确测定煤中砷、硒含量具有重要的理论和实践意义。现有中国国标(GB/T 16415—2008, GB/T 3058—1996)测定煤中总砷、总硒含量为干法分析法，该方法具有操作步骤复杂，误差大的缺陷。为了准确、快速测定煤中总砷、总硒的含量，克服干法分析方法的缺陷，在长期摸索的基础上，借鉴土壤中砷、硒的测试方法，建立了电热板混酸消解-氢化物发生-原子荧光测定煤中总砷、总硒的方法，即湿法分析方法。方法：准确称取0.05～0.10 g煤样(100目)，转移入100 mL玻璃烧杯中，加入10 mL硝酸、2 mL高氯酸，加盖玻璃表面皿，于通风橱中静置过夜。次日，在电热板(180 ℃)上加热消解至白色浓烟冒出，液体透明，残余样品呈白色或者灰白色。取下冷却后，加入6 mol·L-1盐酸溶液3 mL，再次放在电热板上加热消解。当再次有白色浓烟开始冒出时，取下冷却后，加入1 mL浓盐酸。少量亚沸水冲洗烧杯和表面皿内壁，将消解液转移入25 mL试管，亚沸水定容至刻度线，摇匀待测硒;取3 mL消解液，转移入15 mL试管，加入1 mL浓盐酸，1 mL硫脲+抗坏血酸还原剂，亚沸水定容至刻度线，摇匀待测砷;用原子荧光法测定消解液中砷、硒含量。用该方法对煤成分分析标准物质(GBW11115, GBW11117)中砷、硒含量进行测定，测得砷回收率在99.7%～100.3%之间，相对标准偏差范围为5.6%～6.0%;硒相对标准偏差范围为11.1%～13.5%;对应砷和硒的检测限分别为0.05和0.01 μg·L-1。该方法可以准确测定煤中砷、硒含量，且较国标干法分析方法具有操作步骤少、准确性高等优点。

Determination of Total Selenium and Arsenic in Coal by Wet Digestion Hydride Generation Atomic Fluorescence Spectrometry (HG-AFS)

In the present work we presented a new method for determination of total Se and As in coal by electric hot plate-mixed acids-hydride generation atomic fluorescence spectrometry (HG-AFS), the wet digestion method. The detailed operation procedures of the new method are as follows: About 0.05～0.10 g of powdered (200 mesh) coal sample was placed in a glass beaker, 10 mL of nitric acid (HNO₃) and 2 mL of perchloric acid (HClO₄) were added to the beaker in sequence, then the beaker was covered with a watching glass and placed in a fume cupboard standing overnight. The beaker was placed on an electric hot plate (180 ℃) for sample decomposition the next day. The beaker was moved away from the electric hot plate when white smoke arose in the beaker, the sample color turned white or grey and the solution turned clear. Three milliliter of hydrochloric acid (HCl) solution (6 mol·L-1) was added to the beaker after the temperature of the beaker returned to room temperature. The beaker was heated on the electric hot plate again, and then moved away when white smoke started arising again. One milliliter of HCl was added in the beaker after the temperature of the beaker returned to room temperature. After that, the digested sample was transferred to a 25 mL test tube which was filled with ultrapure water to the tube’s full volume. This solution was used for Se determination directly. Three milliliter of the Se test solution prepared above was transferred to a 15 mL glass test tube, 1 mL of thiourea/ascorbic acid solution (2.5 g·mL-1) and 1 mL of the concentrated HCl was added to the 15 mL test tube. The test tube was then filled with ultrapure water to its full volume. The solution was used for As determination after shaking well and 40 min standing. Finally, Se and As concentrations in these prepared solutions were measured by using the AFS-9780 instrument (Beijing Haiguang Instrument Co., LTD, Beijing, China). Two Chinese Coal Certified Reference Materials (GBW11115 and GBW11117) were tested using this method, and the recoveries of As were 99.7%～100.3% and the relative standard deviation (RSD) for As and Se were 5.6%～6.0% and 11.1%～13.5%, respectively. The limits of detection (LOD) of the method for Se and As determination were 0.01 and 0.05 μg·L-1, respectively. These results indicated that this new method was suitable for Se and As determination in coal, and it had the advantages of simple operation, high accuracy and reproducibility compared with the Chinese National Standard method.