Thallium is an environmentally hazardous element because of its toxic effects. It is, therefore, important to detect and determine thallium in a wide range of matrices. Thallium can be found in the nature in two different oxidation states; Tl(I) and Tl(III). It has been shown that, the the lower valency state is more toxic than the trivalent state. Hence, the content of thallium in environmental samples and its speciation are important and should be controlled systematically [1]. Atomic absorption spectrometry (AAS) is a simple, costeffective, and easily available technique, though it suffers from low sensitivity for trace determinations of thallium. A new sensitive electrochemical hydride genration-atomic absorption spectrometric method has been recently introduced by the authors [2] to improve the determination of thallium by AAS. Although this method features high sensitivity, simplicity, rapidness, freedom of reagent, cost-effectiveness, and environmental cleanness, it could not distinguish between Tl(I) and Tl(III) species. So, a pretreatment stage for separation of two oxidant forms is necessary to perform speciation analysis. In this research, a pre-separation stage is proposed for separating the two species in environmental water samples. Amberlite IRC-718 resin with the functional group of iminodiacetic acid [3] is proposed for this step. Adsorption behavior of Tl(I) and Tl(III) on Amberlite IRC-718 was investigated and showed to be strongly pH-dependent. The resin efficiently adsorbed Tl(III) from the sample at all tested pH ranges (1 - 8), while Tl(I) can be completely removed from the samples if the pH value is greater than 4. Thus, it is possible to separate these two forms in the pH range of 1 - 3. Several methods for resin separation have been proposed and compared. These methods include: free resin separation, column separation, and disc separation. Pump-assisted column separation showed the best performance and compatibility for separation and speciation analysis of Tl(I) and Tl(III). The effective parameters on separation efficiency such as type of the buffer and electrolyte solutions, resin weight, sample flow rate, and the acidity of samples have been optimized. In the optimum conditions, >90% adsorption efficiency for Tl(III) and <5% adsorption for Tl(I) were achieved which enable us perform the speciation analysis of thallium. The method was successfully applied to determination and speciation of thallium in environmental water samples.

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