This book will be ideal for young researchers in the field of separation Science, because in this book our developed method gives an idea about separation and spectrophotometric determination of some metal ions found in nature. In order to separate these metal ions in purest form, the proposed solvent extraction method is very useful. The important features of the proposed method: (i) It permits selective separation and determination of Selenium(IV) and Tellurium(IV) from other associated metals such as, Au(III), Sn(IV), Ge(IV), Fe(III) and Pb(II), (ii) Low reagent concentration is required for quantitative recovery of Se and Te. (iii) The extraction occurs in a single stage.(iv) It is free from interference of a large number of foreign ions which are associated with Se(IV) & Te(IV) in its natural occurrence. The selectivity was enhanced by the use of suitable masking agents. (v) The probable stoichiometry of the extracted species calculated to be 1:1 (metal: thiol). The yellow colored complex is stable for more than 48 h. (vi) It is successfully applicable to the determination of Selenium(IV) and Tellurium(IV) in analysis of binary, synthetic mixtures and thin films.