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

摘要

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0.500 g,先后用水20 mL,用0.1 mol·L-1K2HPO4-KH2PO4缓冲溶液(pH 7.0) 10 mL,用0.1 mol·L-1NaOH溶液20 mL和用3 mol·L-1HCl溶液10 mL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HNO31 mL和HF及HClO4各0.5 mL,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6 mol·L-1HCl溶液1 mL溶解残渣并使其中Se(Ⅵ)还原为Se(Ⅳ),将溶液定容至10.0 mL,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10 mL、盐酸浓度0.6 mol·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0.21 μg·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-KH2PO4buffer solution(pH 7.0),20 mL of 0.1 mol·L-1NaOH 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 4th extraction,was dried and transferred into a PTFE vessel,and digested with 1 mL of HNO3,0.5 mL of HF and 0.5 mL of HClO4under 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 with 1 mL of 6 mol·L-1HCl 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(3s/k)found was 0.21 μg·L-1,and RSDs(n=6)found were all less than 11%.Recovery found by standard addition were ranged from 91.7%to 107%.