论文部分内容阅读
环境Pb的测定目前常用的仍是双硫腙(H_2D_z)萃取吸光光度法,由于该体系由被萃取离子Pb~(2+)、萃取螯合剂H_2D_z及萃取溶剂三部分组成,因此萃取溶剂的性质对分析结果影响较大。国内目前常用的萃取溶剂主要有CCl_4和CHCl_3二种,但对二者间的应用选择,尚未见文献统一报道。为此,本文根据方法萃取体系中的平衡关系,对上述二种溶剂进行了选择比较。一溶剂选择弱碱溶液中,Pb~(2+)与H_2D_z在萃取过程中的分配比D为 D=[Pb(HD_z)_2]·{[Pb~(2+)]+[Pb(HD_z)_2]_w}~(-1) =K_(DX)·K_f·K_i~2·K_(DR)~(-2)·[H_2D_z]_0~2·[H~+]~(-2) 上式中,由于螯合常数K_f、H_2D_z离解常数K_i及[H_2D_z]_0、[H~+]等值均相对恒定,故D值的影响主要来
At present, the determination of environmental Pb is still the dithizone (H_2D_z) extraction spectrophotometry. Since this system is composed of the extracted ions Pb 2+, the extraction chelating agent H_2D_z and the extraction solvent, the nature of the extraction solvent The analysis of the greater impact. There are two kinds of extraction solvents commonly used in China currently: CCl_4 and CHCl_3, but there is no unified report on the choice between the two. For this reason, according to the equilibrium relationship in the extraction system of the method, the above two solvents were compared and selected. In a solvent-selective weak alkaline solution, the partition ratio D of Pb 2+ and H 2 D 2 z in the extraction process is D = [Pb (HD_z) _2] · {[Pb 2+] + [Pb (HD_z) _2] _w} ~ (-1) = K_ (DX) · K_f · K_i ~ 2 · K_ (DR) ~ (-2) · [H_2D_z] _0 ~ 2 · [H ~ +] , Since the dissociation constants K_i and [H_2D_z] _0, [H ~ +] have a relatively constant chelation constant K_f and H_2D_z, the influence of D value is mainly due to