分析酸性镀锌溶液中硼酸含量掩蔽剂的选择

Choice of Masking Agents for Analyzing Boric Acid in an Acidic Zinc Plating Bath

目前,测定酸性镀锌溶液中硼酸的方法有几种,不同方法测定结果的差异较大,有些方法的误差是不能允许的。实验表明,不能用柠檬酸钠和EDTA-Na_2掩蔽锌离子。但是,用草酸钠或亚铁氰化钾掩蔽锌离子,能够消除锌离子对测定硼酸的干扰。用甘露醇与硼酸反应生成较强的络合酸,以酚酞作指示剂,用氢氧化钠标准溶液滴定。本法准确度较高,能够满足监控酸性镀锌溶液中硼酸的要求。

At the present time, there are some methods for analyzing boric acid in an acidic zinc plating bath. The determination results obtained with these analysis methods are different, and some errors are not allowable. Experiments show that, the method for masking zinc ions with sodium citrate tribasic or EDTA - Na2, can not be used to analyze boric acid, but masking the zinc ions with sodium oxalate or K4 [ Fe（CN） 6 ] can eliminate influence of the zinc ions on the determination of baric acid. Boric acid reacts with D - mannltol to form complexing acid which has better acidity. And then the determination is carried out with phenolphthalein as indicator by using sodium hydroxide titrimetric method. The method is exact and can satisfy demand for controlling boric acid in an acidic zinc plating bath.