土壤和水系沉积物中硒的价态分析方法研究

Research on the Valence State Analysis Method of Selenium in Soil and Stream Sediment

研究土壤和水系沉积物中硒的价态有助于了解硒(Se)的迁移和转化。目前报道大多只是测定土壤和水系沉积物中部分Se的价态,而如何测定土壤和水系沉积物中全部Se的价态一直是一个难题,难点在于如何将土壤和水系沉积物中的Se消解完全而不改变Se的价态。试验发现6.0 mol·L^(-1) HCl可以将Se(Ⅵ)还原成Se(Ⅳ);而在室温条件下1.2 mol·L^(-1) HCl介质中Se(Ⅳ)和Se(Ⅵ)放置48 h,价态保持不变。Se(Ⅳ)和Se(Ⅵ)采用HNO_(3)+HF+HClO_(4)进行消解,加热到HClO_(4)冒白烟时,Se(Ⅳ)和Se(Ⅵ)的价态保持不变;而土壤和水系沉积物中Se采用HNO_(3)+HF+HClO_(4)进行消解,加热到HClO_(4)蒸干以后,Se(Ⅳ)会被氧化成Se(Ⅵ)。基于以上的研究结果,建立了氢化物发生-原子荧光光谱法(HG-AFS)测定土壤和水系沉积物中Se(Ⅳ)和Se(Ⅵ)的方法,样品采用HNO_(3)+HF+HClO_(4)消解,加热至HClO_(4)冒白烟后停止加热(避免局部蒸干),消解后的样品冷却至室温用1.2 mol·L^(-1) HCl溶解,采用HG-AFS测定得到样品中Se(Ⅳ)。消解后的样品采用6.0 mol·L^(-1) HCl加热溶解,将Se(Ⅵ)全部还原为Se(Ⅳ),采用HG-AFS测定得到样品中总Se,利用差减法得Se(Ⅵ)。测定结果表明土壤和水系沉积物中Se消解完全,Se(Ⅳ)和Se(Ⅵ)在分析过程中价态保持不变,Se(Ⅳ)和总Se的检出限分别为4.5和5.1 ng·g^(-1),Se(Ⅳ)和Se(Ⅵ)加标回收率分别为102%~108%和94%~104%。

The study on the valence state of selenium in soil and stream sediment contributes to understanding the migration and transformation of selenium(Se).At present,there are many methods on the research of valence state of Se extracted partly from soil and stream sediment,but how to determine the valence state of all Se is still a difficult problem and the difficulty lies in how to digest Se in soil and stream sediment completely with valence state unchanged.The research showed that Se(Ⅵ)could be reduced to Se(Ⅳ)by 6.0 mol·L^(-1) HCl and the valence state of Se(Ⅳ)and Se(Ⅵ)stayed stable in 1.2 mol·L^(-1) HCl solution for 48 h at room temperature.Se,in soil and stream sediment,is digested with HNO_(3)+HF+HClO_(4) completely and the valence state of Se(Ⅳ)and Se(Ⅵ)was unchanged when the HClO_(4) heated to white smoke appeared,but after the HClO_(4) heated to dryness,Se(Ⅳ)will all be oxidized to Se(Ⅵ).The method to determine Se(Ⅳ)and Se(Ⅵ)in soil and stream sediment by hydride generation-atomic fluorescence spectroscopy(HG-AFS)was developed based on this research,and the samples were digested with HNO_(3)+HF+HClO_(4) and heated to white smoke appeared,then stopped heating(to avoid local heating to dry).After the digestion,the samples which cool down to room temperature were dissolved with 1.2 mol·L^(-1) HCl,and Se(Ⅳ)can be detected by HG-AFS.The Se(Ⅵ)will all be reduced to Se(Ⅳ)by being heated in 6.0 mol·L^(-1) HCl solvent,and then total Se can be detected by HG-AFS,from the total quantities minus the Se(Ⅳ)concentration we obtained the Se(Ⅵ)concentration.The results show that Se in soil and stream sediment is digested completely and the valence state of Se(Ⅳ)and Se(Ⅵ)stayed stable.The detection limits of Se(Ⅳ)and total Se were 4.5 and 5.1 ng·g^(-1),respectively.The recovery rate of Se(Ⅳ)and Se(Ⅵ)was 102%~108% and 94%~104%.