用光度法研究了镧－邻苯二酚紫（ＰＶ）－溴化十六烷基吡啶（ＣＰＢ）的显色反应。在硼砂－盐酸缓冲体系中，Ｌａ￣（３＋）ＰＶ－ＣＰＢ形成配位比为１∶２∶３的蓝色三元配合物。其最大吸收波长λ＿（ｍａｘ）＝６７３．２ｎｍ，表观摩尔吸光系数：ε＇＝４．３×１０￣４Ｌ·ｍｏｌ￣（－１）·ｃｍ￣（－１）．当Ｌａ￣（３＋）的浓度在０～２０μｇ／１０ｍＬ范围内时符合比尔定律。在碱性条件下该显色反应可测定银合金中的微量镧。 The color reaction of lanthanum - pyrocatechol violet (PV) - cetyl pyridinium bromide (CPB) was studied by spectrophotometry. La (3+) PV-CPB formed a blue ternary complex with a coordination ratio of 1: 2: 3 in borax-hydrochloric acid buffer system. The maximum absorption wavelength λ max (max) = 673.2 nm, apparent molar absorptivity: ε ’= 4.3 × 10 -4L · mol -1 (-1) cm -1. Beer’s law is obeyed when the concentration of La (3+) is in the range of 0 ~ 20μg / 10mL. Under alkaline conditions, this color reaction can be used to determine trace amounts of lanthanum in silver alloys.