论文部分内容阅读
在 pH2.5～3时,用二甲酚橙指示剂,可于大多数二价金属及其他稀土元素(除 Sc,pK_(scY)=23.1)存在下滴定钍(pK_(ThY)=23.2)。但继续在 pH5～6滴定上述其他元素(pK_(Me)=16～18)则不可能,由于钍—EDTA 络合物与二甲酚橙生成颜色反应。用甲基百里酚蓝或儿茶酚紫也是同样情况。这因为 pH 值增加时形或不稳定的钍的羟基络合物,能离解而与指示剂显色,使继续滴定其他元素成为不可能。同样原因用 CyDTA也不行。
Thrombin (pK_ (ThY) = 23.2 is titrated with xylenol orange indicator at pH 2.5 to pH 3 in the presence of most divalent metals and other rare earth elements (except sc, pK_ (scY) = 23.1) ). However, it is not possible to titrate the above other elements (pK_ (Me) = 16 to 18) at pH 5 to 6 because the thorium-EDTA complex forms a color reaction with xylenol orange. The same is true for methylthymol blue or catechin violet. This is because pH-sensitive, time-sensitive or unstable thorium hydroxy complexes can dissociate and colorize the indicator, making it impossible to titrate other elements. The same reason CyDTA not work.