2-(3,5-二溴-2-吡啶偶氮)-5-二乙基氨基苯酚(简称3,5-Br_2-PADAP)是许多金属离子的高灵敏显色剂。贵金属铑和钯均可在磷酸介质中与3,5-Br_2-PADAP。形成蓝紫色络合物,但吸收峰重迭严重。当两者共存时,用经典光度法难以进行直接测定。本文利用导数光度法能分辨重迭吸收峰,提高方法自身选择性的特点,研究了不经分离直接 2- (3,5-dibromo-2-pyridylazo) -5-diethylaminophenol (3,5-Br_2-PADAP) is a highly sensitive developer for many metal ions. Both rhodium and palladium are available in phosphoric acid medium with 3,5-Br_2-PADAP. The formation of blue-purple complex, but the absorption peak overlapping serious. When both coexist, it is difficult to measure directly with classical spectrophotometry. In this paper, the derivative spectrophotometry can distinguish overlapping absorption peaks, improve the selectivity of the method itself, studied without separation directly