钻的显色剂有数十种之多,其中应用较广的是亚硝基酚类和吡啶偶氮类,如常用的亚硝基红盐法灵敏度较低(ε=1.4×10~4)。采用〔2-(5-Br-吡啶偶氮)-5-二乙氨基酚)(5-Br-PADAP)作显色剂,由于试剂结构中吡啶环上的吸电子基—Br、苯酚上—N(C_2H_5)_2的斥电子效应使试剂在与金属离子反应时,形成“带电醌型”螯合物而 There are dozens of color developing reagents, among which nitrosophenols and pyridine azo compounds are widely used. For example, the commonly used nitrosyl red salt method has a lower sensitivity (ε = 1.4 × 10 -4) . The use of [2- (5-Br-pyridylazo) -5-diethylaminophenol) (5-Br-PADAP) as the chromogenic reagent, due to the pyridine structure in the reagent electron-withdrawing group -Br, The repulsive electron effect of N (C_2H_5) _2 causes the reagent to form a “quercetate” chelate while reacting with metal ions