Rapid and selective determination of osmium(IV) by UV-visible spectrophotometry using o-methylphenyl thiourea as a chromogenic chelating ligand: sequential separation of osmium(IV), rhodium(III) and platinum(IV)

The objective of this research work was to develop a simple, highly sensitive and precise method for spectrophotometric determination of osmium(IV). O-Methylphenyl thiourea (OMPT) coordinates with osmium(IV) as a 1:1 (osmium(IV)–OMPT) complex in hydrochloric acid media (0.8 mol l−1). The novelty of the investigated method is instant complex formation at room temperature with no need of heating or standing. The complex is stable for more than 8 days. The method is applicable over a wide linearity range (up to 110 µg ml−1). A low reagent concentration is required (2 ml, 0.009 mol l−1 in ethanol). The complex exhibits maximum absorption in the range of wavelength 510–522 nm and 514 nm was selected for further study. The molar absorptivity was 1.864 × 103 l mol−1 cm−1, Sandell’s sensitivity was 0.102 µg of osmium(IV) cm−2. Proposed method was successfully applied for separation and determination of osmium(IV) from binary and ternary synthetic mixtures containing associated metal ions. A scheme for mutual separation of osmium(IV), rhodium(III) and platinum(IV) is developed.

本研究旨在开发一种简便、高灵敏度且精准的分光光度测定法（spectrophotometric determination），用于四价锇（osmium(IV)）的检测。邻甲基苯基硫脲（O-Methylphenyl thiourea，OMPT）可在0.8 mol·L⁻¹的盐酸介质中，与四价锇以1:1的摩尔比配位形成四价锇-OMPT配合物。本方法的创新点在于可在室温下瞬时完成配合物生成，无需加热或静置；该配合物的稳定性可维持8天以上。本方法的线性范围宽广，最高可达110 μg·mL⁻¹，且仅需低浓度的反应试剂（乙醇溶液中浓度为0.009 mol·L⁻¹，用量2 mL）。该配合物在510~522 nm波长范围内具有最大吸收峰，最终选定514 nm作为后续检测的工作波长。其摩尔吸光系数（molar absorptivity）为1.864×10³ L·mol⁻¹·cm⁻¹，桑德尔灵敏度（Sandell’s sensitivity）为0.102 μg四价锇·cm⁻²。所提出的方法已成功应用于含共存金属离子的二元及三元合成混合物中四价锇的分离与测定，并开发了四价锇、三价铑（rhodium(III)）与四价铂（platinum(IV)）的相互分离方案。