Determination of Arsenic, Mercury, Selenium, Antimony and Bismuth in Soil and Sediments by Water Bath Digestion-Atomic Fluorescence Spectrometry
LIN Hai-lan1, 2, ZHU Ri-long1*, YU Lei2, CHENG Yong-xia3, ZHU Rui-rui2, LIU Pei2, REN Zhan-hong3
1. College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, China
2. Hunan Ecological and Province Environmental Monitoring Center, State Environmental Protection Key Laboratory of Monitoring for Heavy Metal Pollutants, Changsha 410019, China
3. Jiyuan Environmental Monitoring Station, Key Laboratory for Monitoring and Remediation of Heavy Metal Polluted Soils of Henan Province, Jiyuan 454650, China
Abstract：A method for determination of the contents of As, Hg, Se, Sb and Bi in soils and sediments by atomic fluorescence spectrophotometry (AFS) was established by using aqua regia as the dissolved medium. The sample placed in a 50 mL glass colorimetric tube was dissolved with 10 mL aqua regia (1+1), then put the colorimetric tube in a boiling water bath and heated it 2 h, and then removed the colorimetric tube to cool, and then fixed with ultra-pure water and shaken to be tested. Compared with the expensive equipment and the low safety (high temperature and high pressure) of microwave digestion, the water bath digestion method has the advantages of simple equipment, easy operation and high repeatability. Considering that the content of mercury, selenium and bismuth in actual samples is relatively low, the sample after water bath digestion can directly be tested did not pretreat with any more acid or other reagent. The reducing agent (KBH4) is another factor that affects sensitivity. Under the same instrumentation conditions，experiments have shown that the fluorescence intensity for As, Se, Sb and Bi increased first and then decreased as the concentration of KBH4 increased, while the fluorescence intensity for Hg increases as the concentration of KBH4 decreases. In this study, when the concentration of KBH4 is 0.1%, it can get good sensitivity to detect Hg. In order to verify the reliability of the method, the effects of different pre-reducing agents to detect Se in soil and sediments were compared. The data showed that the amount of hydrochloric acid used in the digestion was sufficient to reduce Se(Ⅵ) to Se(Ⅳ), and it is not necessary to add hydrochloric acid or thiourea, but it makes the results much lower when the thiourea added into the sample. Under the optimal experimental conditions, the detection limit (LOD) found were 0.008 mg·kg-1 (for As)，0.002 mg·kg-1 (for Hg and Se)，0.005 mg·kg-1 (for Sb) and 0.003 mg·kg-1 (for Bi) (sample quantity 0.500 0 g, sample volume 50 mL), and the limit of quantitation (LOQ) found were 0.032 mg·kg-1 (for As)，0.008 mg·kg-1 (for Hg and Se)，0.020 mg·kg-1 (for Sb) and 0.012 mg·kg-1 (for Bi). The relative error ranges for the determination of As, Hg, Se, Sb and Bi in soil/sediment standard samples were -3.3%~4.5%, -3.9%~15.4%, -20.2%~7.8%, -13.0%~3.4% and 2.2%~7.0%, respectively. The relative standard deviation range for the determination of actual samples was 0.4%~10.3%. The method has the advantages of simplicity of operation, no need for transfer of containers, high accessibility, low detection limits, high precision and accuracy. The method also can satisfy the analysis requirement of environmental monitoring.
Key words：Water bath digestion；Atomic fluorescence spectrometry；Soil and sediments；As/Hg/ Se/Sb/Bi
