STUDY OF THE EXTRACTION AND BACK-EXTRACTION KINETICS OF NI-1-PHENYL-3-METHYL-4-BENZOYL-5-PYRAZOLONE AND THE CORRELATION BETWEEN KINETICS AND CENTRIFUGAL PARTITION CHROMATOGRAPHIC EFFICIENCIES

The interfacial activity of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone ( HL) and its complexation kinetics with Ni(II) in the chloroform-water phase pair have been studied. The interfacial activities are in the or der NiL2 > L- > HL. The rate limiting step in the complexation of Ni(I I) by L- is the formation of NiL+, and the interfacial rate constant i s 4 times larger than the bulk value. The rate limiting step in the ba ck-extraction (dissociation) of NiL2 is the reaction of NiL+ with prot on, and the bulk and interfacial rate constants for this reaction are essentially the same. The dissociation reaction in neutral micelles fo rmed by the surfactant Brij 35 occurs mainly at the aqueous-micellar i nterface with a rate constant that is similar to that at the CHCl3-H2O interface. The band widths of Ni(II) in centrifugal partition chromat ography (CPC), with HL in the CHCl3 stationary phase, are mainly due t o the slow kinetics of back-extraction of NiL2. The CPC inefficiency a s measured by the quantity channel equivalent of a theoretical plate ( CETP) bears a direct correlation to the half-lives of the back-extract ion reaction. This correlation, for the first time, enables the determ ination of the interfacial areas generated, and hence the average size of the mobile phase droplets, in the CPC experiments.