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本文报道了一个灵敏度高、选择性好的测定痕量钍的新光度分析法。在聚乙烯醇（ＰＶＡ）存在下，钍钼杂多酸和丁基罗丹明Ｂ（ＢＲＢ）形成离子缔合物，其适宜条件为ｃＨＣｌＯ４＝１．３ｍｏｌ／Ｌ，ｃＭｏＯ４２－＝６．８×１０－４ｍｏｌ／Ｌ，ｃＢＲＢ＝２．７×１０－５ｍｏｌ／Ｌ，ＰＶＡ０．０８％。络合物的最大吸收波长为５７０ｎｍ，服从比耳定律范围０～０．８ｍｇ／２５ＬＴｈ，表观摩尔吸光度ε为３．６３×１０６Ｌ·ｍｏｌ－１·ｃｍ－１，测定极限１．８μｇ／Ｌ（ｎ＝１２），对０．０２ｍｇ／ＬＴｈ分析１１次的相对标准偏差为２．９％，络合物的摩尔组成Ｔｈ∶Ｍｏ∶ＢＲＢ＝１∶１２∶７。大多数常见元素、１００倍Ｃｅ（Ⅲ）、４０倍Ｕ（Ⅵ）和２０倍Ｐ（Ⅴ）不干扰钍的测定。本法已用于地质标样中钍的测定，结果满意。
In this paper, a new high sensitivity, good selectivity for the determination of trace thorium spectrophotometry. In the presence of polyvinyl alcohol (PVA), heteropolyacid thorium and butyl rhodamine B (BRB) to form ion-association, the appropriate conditions for cHClO4 = 1.3mol / L, cMoO42- = 6.8 × 10 -4 mol / L, cBRB = 2.7 × 10 -5 mol / L, PVA 0.08%. The maximum absorption wavelength of the complex was 570 nm, which obey the Beer’s law range of 0 ~ 0.8mg / 25LTh, the apparent molar absorptivity ε was 3.63 × 106L · mol-1 · cm-1 and the limit of determination was 1.8μg / L (N = 12). The relative standard deviation of the 11 analyzes of 0.02 mg / LTh was 2.9%. The molar composition of the complex was Th: Mo: BRB = 1:12:7. Most common elements, 100 times Ce (III), 40 times U (VI) and 20 times P (V) do not interfere with the determination of thorium. This method has been used for the determination of thorium in geological standards with satisfactory results.