Predominance zone diagrams and their application to solvent extraction techniques

Predominance zone diagrams have been useful tools in solving problems in an alytical chemistry. They can be used to establish the best conditions for s eparation of mixtures or to optimize recovery procedures for a given specie s. The few reports on predominance zone diagrams for the participant specie s in liquid-liquid extraction systems, describe their construction as diagr ams of the Pourbaix type (epsilon/pH). With the generalized species and equ ilibria method (GSEM) it is possible to elaborate Predominance zone diagram s for extraction (PZDE) in proper spaces and with parameters strictly relat ed to these processes such as pH and the volume ratio, r. Therefore, using the GSEM, PZDE that allow us to determine the best conditions for the extra ction of a given substance have been elaborated. The stoichiometry of the s pecies been extracted can also be determined from the experimental conditio ns. It has been demonstrated that with the GSEM, PZDE can be constructed fo r systems of one and two components. In this work, we intend to demonstrate that the algorithm is valid for the elaboration of PZDE in systems of thre e and four components. Examples of analytical interest are presented such a s lead (II) extraction with diphenyltiocarbazone (dithizone) and that for c admium (II) with 8-hydroxyquinolein (oxine) in chloroform. The influence of a masking agent, the etilendiaminotetraacetic acid (EDTA) over the extract ion of both metals was also assessed. (C) 2000 Elsevier Science B.V. All ri ghts reserved.