研究了显色剂 2 -(5 -溴 -2 -吡啶偶氮 ) -5 -二乙氨基苯酚 (简称 5 -Br-PADAP)与铁 (Ⅱ )显色反应的条件 ,在pH =5 .0的醋酸钠 -醋酸缓冲体系中 ,采用非离子表面活性剂OP增溶增敏。铁 (Ⅱ )与显色剂形成的配合物的组成为M∶R =1∶2 ,其lgβ2 =17.74,最大特征吸收峰位于 743.2nm ,表观摩尔吸光系数ε =2 .82× 10 4L·mol- 1 ·cm- 1 。铁 (Ⅱ )含量在 0～ 30ug/2 5mL范围内能很好地服从比耳定律。该法操作简单 ,准确且选择性良好。可用于水样中微量价态铁的测定 ,结果令人满意 The conditions for the color reaction of chromogenic reagent 2 - (5 - bromo - 2 - pyridylazo) -5 - diethylaminophenol (abbreviated as 5 - Br - PADAP) with iron (Ⅱ) Sodium acetate - acetate buffer system, the use of non-ionic surfactant OP solubilization sensitization. The complex of iron (Ⅱ) and chromogenic agent has the composition of M: R = 1: 2, lgβ2 = 17.74, the maximum characteristic absorption peak at 743.2nm and the apparent molar absorptivity ε = 2.82 × 10 4 L · mol-1 · cm-1. The iron (Ⅱ) content in the range of 0 ~ 30ug / 2 5mL can be well obey Beer’s law. The method is simple, accurate and selective. It can be used for the determination of trace valence iron in water samples with satisfactory results