顺序提取分离-氢化物发生-原子荧光光谱法测定富硒土壤中5种形态硒的含量

HG-AFS Speciation Analysis for 5 Species of Selenium in Se-Rich Soil with Separation by Sequential Extraction

用改进的顺序提取分离了富硒土壤样品中5种化学形态的硒(即水溶态、可交换态、有机结合态、酸溶态和残渣态),然后用氢化物发生-原子荧光光谱法(HG-AFS)测定它们的含量。取土壤样品0.500g,先后用水20 mL,用0.1 mol·L^(-1)K_2HPO_4-KH_2PO_4缓冲溶液(pH 7.0)10mL,用0.1mol·L^(-1) NaOH溶液20mL和用3mol·L^(-1) HCl溶液10mL振荡提取。每次提取后,将混合物离心分离。所得的上清液中分别含有上述前4种形态的硒,保留这4份上清液供HG-AFS分析;离心分离后的残渣用于下一步的提取。第4次提取并离心后所得残渣经烘干后移入PTFE罐中,加入HNO_31mL和HF及HClO_4各0.5mL,在密闭加压条件下进行消解。消解完成时,冷却并取出PTFE罐,将其中溶液蒸干,用6mol·L^(-1) HCl溶液1mL溶解残渣并使其中Se(Ⅵ)还原为Se(Ⅳ),将溶液定容至10.0mL,用HG-AFS测定其中的硒量。前3次提取所得上清液,在分别进行HG-AFS测定前均须将溶液转化为总体积10mL、盐酸浓度0.6mol·L^(-1)的试液。按上述5份溶液中所测得的硒量即得样品中5种形态的硒含量。方法的检出限(3s/k)为0.21μg·L^(-1),测定值的相对标准偏差(n=6)均小于11%,加标回收率为91.7%~107%。

The sequential extraction was modified and applied to the speciation analysis of 5 species of selenium in samples of Se-rich soil by HG-AFS.For separation of the 5 species（i.e.,the water-soluble species,the exchangeable species,the organic-bound species,the acid-soluble species and the residual species）,0.500 g of the soil sample was taken and extracted in succession by swirling with 20 mL of water,10 mL of 0.1 mol·L^-1 K2HPO4-KH2PO4 buffer solution（pH 7.0）,20 mL of 0.1 mol·L^-1 NaOH solution and 10 mL of 3 mol·L^-1 HCl solution.After each extraction,the mixtures were centrifuged,the supernatants containing respectively the former 4 species were reserved for HG-AFS determinations,and the residues were collected for the next extraction.The residue,remained after the 4 th extraction,was dried and transferred into a PTFE vessel,and digested with1 mL of HNO3,0.5 mL of HF and 0.5 mL of HClO4 under tight closing and pressure.After digestion,the PTFE vessel was cooled and taken out,and the solution in it was evaporated to dryness.The residue was taken up with1 mL of 6 mol·L^-1 HCl solution and let Se（Ⅵ）be reduced to Se（Ⅳ）.The solution was diluted to 10.0 mL with water,and residual species of Se were determined by HG-AFS.The supernants,obtained in the former 3 extractions,should be treated separately to convert into solutions of 10 mL with concentration of 0.6 mol·L^-1 HCl,before used for HG-AFS analysis.Amounts of Se found in the 5 solutions,represented the contents of 5 species of Se in the soil sample.Value of detection limit（3 s/k）found was 0.21μg·L^-1,and RSDs（n=6）found were all less than 11%.Recovery found by standard addition were ranged from 91.7%to 107%.