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利用铈的变价以及Ｃｅ（Ⅳ）－Ｔｉｒｏｎ配合物在不同酸度条件下颜色的特殊性，建立了无需预先分离而直接测定混合稀土中铈含量的分光光度法。在ｐＨ为９．０条件下，借助空气的氧化，Ｃｅ（Ⅲ）和Ｃｅ（Ⅳ）都与Ｔｉｒｏｎ形成Ｃｅ（Ⅳ）－Ｔｉｒｏｎ配合物。该配合物在ｐＨ为５．０时呈亮黄色，在４３５ｎｍ处有最大吸收。铈的浓度在０～８０μｇ范围内，符合Ｂｅｅｒ定律：摩尔吸光系数ε＝１．６４×１０３Ｌ／（ｍｏｌ．ｃｍ－１；检出限为１．８８μｇ／ｍＬ；线性回归方程为Ａ＝０．０１１７Ｃ－０．０１８（Ｃ以μｇ／ｍＬ表示），线性相关系数γ＝０．９９９２。对稀土样品平行测定６次，变异系数ＣＶ≤２．３％。共存的轻稀土离子对铈的测定无干扰。用于稀土氧化物及稀土盐中铈的测定，结果与ＫＭｎＯ４法比较，相对误差≤０．５５％。
Based on the change of cerium and the particularity of the color of Ce (Ⅳ) -Tiron complex under different acidity conditions, a spectrophotometric method was established for the direct determination of cerium content in mixed rare earth without prior separation. At pH 9.0, both Ce (Ⅲ) and Ce (Ⅳ) formed Ce (Ⅳ) -Tiron complex with Tiron by air oxidation. The complex showed a bright yellow color at pH 5.0 and a maximum absorption at 435 nm. The concentration of cerium in the range of 0 ~ 80μg, in line with Beer’s Law: molar extinction coefficient ε = 1.64 × 103L / (mol.cm-1; detection limit of 1.88μg / mL; linear regression equation A = 0117C-0.018 (C in μg / mL), the linear correlation coefficient γ = 0.9992. The samples were measured 6 times in parallel and the coefficient of variation CV was less than or equal to 2.3%. The coexistence of light rare earth ions on the determination of cerium Interference. Used for the determination of rare earth oxides and rare earth salts of cerium, the results compared with the KMnO4 method, the relative error ≤ 0.55%.