研究了在阳离子表面活性剂 CTMAB存在下 ,Fe( )与 2 - (5-溴 - 2 -吡啶偶氮 ) - 5-二乙氨基苯酚 (5-Br- PADAP)的显色反应。试验表明 ,在 p H=3.6— 6 .4范围内 ,Fe( )与 5- Br- PADAP形成稳定的红色络合物 ,最大吸收峰位于 559nm和 74 9nm。在 74 9nm处 ,络合物的表观摩尔吸光系数为 3.1× 10 4 L·mol-1· cm-1,组成比为 Fe( )∶ 5- Br- PADAP=1∶ 3,铁量在 0— 50 μg/ 2 5m L范围内符合比耳定律。方法选择性较高 ,用于水样中微量铁的测定 ,结果令人满意 The color reaction of Fe () with 2 - (5 - bromo - 2 - pyridylazo) - 5 - diethylaminophenol (5 - Br - PADAP) was studied in the presence of cationic surfactant CTMAB. Experiments show that Fe () and 5-Br-PADAP form a stable red complex in the range of p H = 3.6-6.4 with maximum absorption peaks at 559 nm and 749 nm. The apparent molar absorptivity of the complex at 74 9 nm was 3.1 × 10 4 L · mol -1 · cm -1, the composition ratio was Fe () 5-Br-PADAP = 1, the amount of iron was 0 -50 μg / 2 5m L Beer’s law is valid. The method has high selectivity and is suitable for the determination of trace iron in water samples with satisfactory results