一阶导数分光光度法同时测定水样中Cr(Ⅲ)和Cr(Ⅵ)

徐红纳; 靳立国; 由丽梅; 程艳

doi:10.15898/j.cnki.11-2131/td.201908090118

一阶导数分光光度法同时测定水样中Cr(Ⅲ)和Cr(Ⅵ)

Simultaneous Determination of Chromium(Ⅲ) and Chromium(Ⅵ) in Water by the First Derivative Spectrophotometric Method

摘要

摘要: 环境水样中的铬通常以Cr（Ⅲ）和Cr（Ⅵ）的形态存在，不同价态的铬产生不同的生理作用，对不同价态铬进行准确分析是必要的。目前Cr（Ⅲ）和Cr（Ⅵ）的测定方法大多数是先分离后再测定，或先测定出Cr（Ⅲ）或Cr（Ⅵ），然后通过氧化或还原测定铬的总量，再差减法计算出另一价态铬的含量，此操作复杂，并且在处理过程中易导致价态的改变，误差较大，精确度难以保证。本文用一阶导数分光光度法消除了Cr（Ⅲ）对Cr（Ⅵ）干扰，能同时测定Cr（Ⅲ）或Cr（Ⅵ）的含量。混合水样中加入显色剂EDTA-2Na，调节溶液pH在3~3.5，恒温水浴70℃条件保持加热15min，测定吸光度，导数间隔因子为10nm求一阶导数，在波长330nm处Cr（Ⅵ）吸光度一阶导数有最大值，而在此波长处Cr（Ⅲ）-EDTA络合物吸光度一阶导数值为0，可用一阶导数分光光度法测定Cr（Ⅵ）的含量，在Cr（Ⅲ）-EDTA的最大吸收波长543nm处测溶液吸光度，直接测定Cr（Ⅲ）的含量。在优化实验条件下，Cr（Ⅲ）线性回归方程为A=0.0036ρ-0.0002（r²=0.9999），线性范围为0~120mg/L，检出限为0.006mg/L；Cr（Ⅵ）线性回归方程为D=0.00072ρ-0.00013（D为一阶导数值，r²=0.9996），线性范围为0~100mg/L，检出限为0.005mg/L。Cr（Ⅲ）和Cr（Ⅵ）加标回收率为97.8%~102.6%。该方法能够满足废水中Cr（Ⅲ）和Cr（Ⅵ）分析测试要求。

Abstract:
OBJECTIVESChromium is usually found as Cr(Ⅲ) and Cr(Ⅵ) in environmental water samples. The different valences of chromium produce different physiological function, thus it is necessary to analyze the different valences of chromium accurately. At present, the contents of Cr(Ⅲ) and Cr(Ⅵ) are mostly determined after separation or the content of Cr(Ⅲ) or Cr(Ⅵ) is measured first, then the total content of Cr is determined after oxidation or reduction. The content of another valence of chromium is then calculated by the subtraction method. The available method needs a complex procedure. Moreover, the valence of Cr is easily modified during the sample treatment, resulting in large error and low precision.
OBJECTIVESTo find a simple and accurate method for determination of Cr(Ⅲ) and Cr(Ⅵ).
METHODSThe first derivative spectrophotometric method was used for simultaneously determining of Cr(Ⅲ) and Cr(Ⅵ), which eliminated the interference of Cr(Ⅲ) on Cr(Ⅵ).
RESULTSChromogenic reagent EDTA-2Na was added to the mixed water sample in a 70℃water-bath at pH 3-3.5 for 15min, and the absorbance was measured. When the derivative interval factor was 10nm, the first derivative value of absorption for Cr(Ⅵ) was the maximum at 330nm wavelength and the value for Cr(Ⅲ)-EDTA was zero. The concentration of Cr(Ⅵ) can be obtained by the first derivative spectrophotometric method, whereas Cr(Ⅲ) can be determined directly at the maximum wavelength of 543nm. Under the optimal conditions, the concentration range was 0-100mg/L for Cr(Ⅵ) and 0-120mg/L for Cr(Ⅲ). The equation of linear regression for Cr(Ⅲ) was A=0.0036ρ-0.0002 (r²=0.9999), for Cr(Ⅵ) was D=0.00072ρ-0.00013 (r²=0.9996). and the limit of detection was 0.005mg/L for Cr(Ⅵ) and 0.006mg/L for Cr(Ⅲ). The recoveries for Cr(Ⅲ) and Cr(Ⅵ) were 97.8%-102.6%.
ConclusionThe method meets the requirements for analyzing waste water.

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