铁对地下水中六价铬测定的影响

Influence of Iron on Determination of Hexavalent Chromium in Groundwater

六价铬对人体具有致癌作用,准确定量水质中六价铬的质量浓度尤为重要。二苯碳酰二肼分光光度法测定六价铬的过程中有许多干扰因素,其中铁元素的干扰尤为明显。着重考察了不同质量浓度二价铁、三价铁对分光光度法测定水质中六价铬的影响,并对影响的消除作了初步的探究。当水中二价铁质量浓度低于六价铬的1.5倍时,不影响六价铬的测定,当二价铁质量浓度继续增大时,会对六价铬的检测产生显著影响;研究发现,在含有二价铁的水中,二价铁和六价铬的质量浓度比例为1.5时,二价铁开始干扰六价铬的测定,但在实际水样中,二价铁存在非常短暂,可以将其转化为三价铁进行消除干扰;水中三价铁质量浓度大于六价铬的10倍时,会干扰六价铬的测定,可以通过加入适量的磷酸,调节溶液的酸度为8.0~9.0,采用弱酸性的显色剂,可完全去除干扰。

Hexavalent chromium has carcinogenic effect on human body,so it is very important to accurately quantify the mass concentration of hexavalent chromium in water quality.There are many interference factors in the determination of hexavalent chromium by diphenylcarbonyl hydrazine spectrophotometry,among which the interference of iron element is particularly obvious The influence of ferric iron on spectrophotometric determination of chromium hexavalent in water quality was analyzed,and the elimination method of the influence was discussed.The results showed that,when the mass concentration of ferric iron in water was less than 1.5 times of chromium hexavalent,ferric iron did not affect the determination of chromium hexavalent;when the mass concentration of ferric iron continued to increase,it had a significant influence on the detection of chromium hexavalent.It was found that when the mass concentration ratio of iron divalent to chromium hexavalent in water containing iron divalent was 1.5,iron divalent began to interfere with the determination of chromium hexavalent,but in the actual water sample,iron divalent existed very briefly and could be converted into trivalent iron to eliminate the interference.When the mass concentration of ferric iron in water was more than 10 times of hexavalent chromium,it could interfere with the determination of chromium hexavalent.The interference could be completely removed by adding appropriate phosphoric acid to adjust the acidity of the solution to 8.0~9.0 and using weak acid chromogenic agent.