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Spectrophotometric Study of Osmium-Thiocyanato Complexes in the Presence of Surfactants

An aqueous solution of the nonionic surfactant Triton X-100, when heated above the cloud-point temperature, exhibits the property of separating into an aqueous phase and a surfactant-reach phase. This phase-separation phenomenon can be used for extraction of metal complexes. In order to throw more light on the influence of surfactants on the spectrophotometric properties of metal complexes we have studied the extraction of osmium thiocyanate. When an acidic aqueous solution of osmium(VIII) containing thiocyanate ions was heated, an orange-yellow complex was formed. The complex could be extracted as ion-pair with cetylpyridinium chloride (CPC) to chloroform as well as in the surfactant-reach phase of Triton X-100. In view of good reducing properties of thiocyanate, the reduction of osmium(VIII) with excess of thiocyanate by heating, was taken in to account. The extracted osmium– thiocyanato complex had maximum absorption at 445 nm and followed Beer´s law in the range of 2´10-5 - 1.2´10-4 M osmium(VIII). The respective molar absorptivities depended on extraction conditions. The results of investigation of the surfactant-extraction system of the osmium-thiocyanato complex in Triton X-100 were compared with those obtained in the usual liquid-liquid extraction system using chloroform as organic solvent.

extraction; hexadecylpyridinium chloride (CPC); osmium; spectrophotometry; thiocyanate; Triton X-100

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