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Cr(Ⅵ)是十分有害的环境致癌物质,系环境研究中的重要监测对象。微量Cr(Ⅵ)的测定,常用二苯卡巴肼光度法,而有关偶氮类(变色酸双偶氮类)试剂与Cr(Ⅵ)褪色反应的研究近年已有报道。本工作研究了于H_2SO_4,介质中CPA-pA与Cr(Ⅵ)褪色反应的光度性质,据此可进行Cr(Ⅵ)的测定。方法的表观摩尔吸光系数为1.95×10~4,在酸度为0.01～3.0mol·L~(-1)H_2SO_4介质中沸水浴加热5min,即可褪色完全,Cr(Ⅵ)1～25μg/25ml遵从比耳定律。本法的选择性较好,体系稳定,操作简便。 1 试验部分 1.1 主要仪器与试剂 721型分光光度计 DMS-300型分光光度计(美国瓦利安) Cr(Ⅵ)标准溶液:以K_2Cr_2O_7(A.R)按常规法配成Cr(Ⅵ)1.000mg·ml~(-1)的储备液,再将此溶液逐级稀释至2.0μg·ml~(-1)的工作溶液。
Cr (VI) is a very harmful environmental carcinogen, which is an important monitoring object in environmental studies. Determination of trace Cr (Ⅵ), commonly used diphenylcarbazide spectrophotometry, and the azo (chromotropic acid disazo) reagent and Cr (Ⅵ) discoloration reaction has been reported in recent years. In this work, the photometric properties of the fading reaction between CPA-pA and Cr (Ⅵ) in H_2SO_4 medium were studied, and the determination of Cr (Ⅵ) was carried out. The apparent molar absorptivity of the method is 1.95 × 10 ~ 4. When the acidity is 0.01 ~ 3.0mol·L ~ (-1) H_2SO_4 and heated in a boiling water bath for 5min, the fading is complete. Cr (Ⅵ) 1 ~ 25μg / 25ml Comply with Beer’s Law. The selectivity of this Law is better, the system is stable and the operation is simple. 1 Experimental 1.1 Main Equipment and Reagents 721 Spectrophotometer DMS-300 Spectrophotometer (Walliser, USA) Standard solution of Cr (Ⅵ): K 2 Cr 2 O 7 (AR) was used to prepare 1.000 mg · ml ~ (-1) stock solution, and then dilute the solution to 2.0μg · ml -1 working solution.