Extraction spectrophotometric determination of elements in form of ion-association compounds of metal chaltes and dyes. Pt. 2. The system cobalt-5, 7-dichloro-8-hydroxyquinoline-rhodamine 6G, benzene

The extraction of the ion-pair formed by the anionic, coordinatively saturated complex of cobalt with 5,7-dichloro-8-hydroxyquinoline (Cl2HOx) and Rhodamine 6G cation (ROD+) was investigated. The cobalt ions at the concentration 4 x 10-5M are fully extractable at pH=6.3; 1 x 10-3 M Cl2HOx and 4 x 10-4 M Rhodamine 6G after 10 minutes of extraction. In absence of Rhodamine 6G the cobalt complexes are not extractable. The extractable ion-pair has the composition according to the formula Co(Cl2Ox)3-.ROD+. The molar absorptivity at lambda=542 nm is equal to 7.5 x 104. The extraction constant log Ksub(ex)=0.44+-0.14. The protonation constant of Rhodamine (log K=-0.98+-0.08) and two-phase stability constant of the carbinol base of Rhodamine 6G (log β = 5.35. +- 0.04) were also calculated. (author)