[Determination of Total Selenium and Arsenic in Coal by Wet Digestion Hydride Generation Atomic Fluorescence...

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 °C) 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 HCI 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.