二亚乙基三胺五乙酸修饰的固体汞合金电极测定铬(Ⅵ)和无机态铬(Ⅲ)

Determination of Cr(Ⅵ) and Inorganic Cr(Ⅲ) using Solid Amalgam Electrode Modified with DTPA

介绍了一种基于Cr(Ⅲ)-二亚乙基三胺五乙酸(DTPA)-NO3-体系的催化作用测定溶液中铬(Ⅵ)和无机态铬(Ⅲ)的方法。制作了银汞合金电极,并在其表面通过自组装修饰上DTPA。在含有0.1mol/LHAc-NaAc(pH=5.5)缓冲液和0.25mol/L KNO3溶液中,当电极电位在-0.80^-1.40V间进行阴极化扫描时,溶液中Cr6+在电极表面被还原成为Cr3+并与电极表面上的DTPA络合,同时溶液中无机态铬(Ⅲ)也与DTPA络合,于-1.24V左右形成灵敏的还原峰。通过改变扫描前富集方式,分别实现铬(Ⅵ)和无机态铬(Ⅲ)的测定。铬(Ⅵ)和无机态铬(Ⅲ)的线性范围分别为:5.0×10-9~5.0×10-6mol/L和1.0×10-8~5.0×10-6mol/L,检测限为1.6×10-10mol/L和5.1×10-9mol/L。对溶液进行11次平行测定相对标准偏差为4.3%。该法用于实际水样测定,Cr(VI)和Cr(Ⅲ)的标准加入回收率为98.5%~105.0%。

Solid silver-amalgam electrode modified with dieth acid （DTPA） has been fabricated to detect chromium species utilizing the electrode surface DTPA pre-extraction and the catalytic system Cr（ Ⅲ）- DTPA-NO3^- . Cr（Ⅵ） in solution has been reduced to Cr（Ⅲ） and pre-concentrated on the surface of the electrode to form complex,and then,Cr（ Ⅲ ）-DTPA complex is reduced and a sensitive reduction peak was produced at - 1.24V when the potential scanned in the range of at - 0.8 - - 1.4V. The determination conditions i.e. supporting electrolyte, pH values, accumulation-time,were investigated and optimized. In the range of 5 × 10-9 - 5 ×10-6mol/L and 1 × 10^-8-5 × 10-6mol/ L the dependence of the peak current on the Cr（ Ⅵ ） and inorganic Cr（ Ⅲ ） concentrations were linear respectively. The detection limits of them were 1.6 × 10^-10mol/L and 5.1 × 10^-9 mol/L. The results indicated that this modified electrode was effective for the determination of trace amount of Cr（ Ⅵ ） and inorganic Cr（ Ⅲ ）.