Analytical Sciences

A New Selective Chromogenic Reagent for the Spectrophotometric Determination of Thallium(I) and (III) and Its Separation Using Flotation and the Solid-Phase Extraction on Polyurethane Foam

Khaled S. ABOU-EL-SHERBINI,* Gamal A. E. MOSTAFA,** and Mohamed M. HASSANIEN*** 

*Department of Inorganic Chemistry, National Research Centre, Dokki, Cairo, Egypt
**Microanalytical Laboratory, Department of Applied Organic Chemistry, National Research Centre, Dokki, Cairo, Egypt
***Department of Chemistry, Industrial Education College, Beni-Suef, Egypt

A new sensitive chromogenic reagent, 9,10-phenanthaquinone monoethylthiosemicarbazone (PET), has been synthesized and used in the spectrophotometric determination of Tl(III). In HNO₃, H₂SO₄ or H₃PO₄ acids, PET can react immediately at room temperature with Tl(III) to form a red 2:1 complex with a maximum absorption at 516 nm. The different analytical parameters affecting the extraction and determination processes have been examined. The calibration curve was found to be linear over the range 0.2 - 10 ug cm^-3 with a molar absorptivity of 2.2 x 10⁴ dm³ mol^-1 cm^-1. Sandell's sensitivity was found to be 0.0093 ug cm^-2. No interference from macroamounts of foreign ions was detected, except for Pd(II). However, Pd(II) does not affect the determination process, because its complex with PET has its lambda_max at 625 nm. The proposed method has been applied to the determination of Tl(I and III) in synthetic and natural samples after separation by flotation (in oleic acid/kerosene) and solid-phase extraction (on polyurethane foam) techniques. The two methods were found to be accurate and not subject to random error, but solid-phase extraction was preferred because it is cheap, simpler and there is no contamination risk coming from flotation reagents.

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