2-(4-氯-2-膦酸基苯偶氮)-7-(4-碘苯偶氮)-1,8-二羟基萘-3,6—二磺酸(简称对碘偶氮氯膦)在0.1N盐酸介质中,能与稀土元素立即形成蓝色络合物。此络合物的最大吸收峰在680nm处,具有显色酸度范围宽、灵敏度高、选择性较好以及对各个稀土元素形成的络合物的摩尔吸光系数ε=(9.7～10.8)×10~4基本一致等优点,这就为测定钢铁中的稀土总量提供了有利条件。 2- (4-chloro-2-phosphonophenylazo) -7- (4-iodophenylazo) -1,8-dihydroxynaphthalene-3,6-disulfonic acid Phosphine) is capable of forming a blue complex with a rare earth element immediately in a 0.1 N hydrochloric acid medium. The maximum absorption peak of this complex at 680nm, with a wide range of chromogenic acidity, high sensitivity, good selectivity and the molar absorptivity ε (9.7 ~ 10.8) × 10 ~ 4 basically the same advantages, which provides a favorable condition for the determination of the total amount of rare earths in steel.