RESUMO
Several techniques are used for the determination of Th, U and La in different media. But these techniques are limited considering the performance, including UV/VIS Spectrophotometer, X-ray fluorescence spectrometry, atomic absorption and emission spectrometry [1,2]. The atomic absorption spectrometry isn't applicable for the determination of Th and U because of the non-availability of the hollow cathode lamps[3]. Strong claims are made for the specificity and sensitivity of NAA, ICP-AES and ICP-MS, inspite of the fact that interference is a problem using these techniques. Hence the application of organic reagents for the spectrophotometric determination of these elements is well-known and continues to be applied[4]. Several organic and inorganic reagent have been reported for the spectrophotometric determination of Th, U, and La[5,6]. Arsenazo I is considered to be suitable for the spectrophotometric determination for many elements because it is commercially available and is water-soluble. The reagent has ability to form stable complexes in strong acidic and basic media. Th, U and La often coexist in ores like monazite and other minerals and their selective determination is a problem in analytical chemistry[4] therefore the aim of the present investigation is to establish a procedure for the selective determination of Th, U, and La depending on pH adjustment