萃取分光光度法测定痕量六价铬的研究

Study on determination of trace chromium(Ⅵ) by extractive spectrophotometry

pH为2．0的氯化钾一氯化氢缓冲溶液中，在常温下，六价铬与二苯偶氮羰酰肼（DPCO）反应生成稳定的络合物（六价铬与DPCO物质的量比为1：2），在硫酸铵的作用下，该络合物中的六价铬可被聚乙二醇（PEG）相全部萃取，据此建立了测定痕量六价铬的新方法——萃取光度法。结果表明，在PEG相中络合物的最大吸收波长为548nm，六价铬质量浓度在0—2．5mg／L内符合比尔定律，方法的表观摩尔吸光系数为3．12×10^4L／（mol·cm），多数常见离子不干扰测定。方法用于硝酸铬及氯化铬中痕量六价铬的测定，得到满意的结果。

A new extractive spectrophotometry for determination of trace chromium （ VI ） was established. In KCl - HCI buffer solution of pH = 2.0 and at the room temperature, chromium （ Wl ） could react with diphenylearbazone （ DPCO ） to form a stable complex [ n（ Or（VI） ） ： n（DPCO） = 1：2 ], and Cr（VI ） in Cr（ VI ） - DPCO complex can be extracted by PEG - （NH4 ）2SO4 completely. Results showed that the maximum absorption wavelength of the complex in PEG phase was 548 nm with the apparent molar absorptivity of 3.12 × 10^4 L/（ mol · cm ） ;Beer＇s law was obeyed in the mass concentration range of 0 -2.5 mg/L for Cr（ VI ） ;Most of common ions did not interfere in the determination of chromium（ VI ）. This proposed method has been applied in the determination of trace chromium （ VI ） in chromic nitrate and chromic chloride with satisfactory results.