Flame Atomic Absorption Spectrometric Determination of Trace Amounts of Cobalt after Cloud Point Extraction as 2-[(2-Mercaptophenylimino)methyl]phenol Complex

A cloud point extraction (CPE) procedure was developed for the separation and preconcentration of trace amounts of cobalt prior to its determination by flame atomic absorption spectrometry (FAAS). The procedure is based on the formation of Co(II) complex with 2-[(2-mercaptophenylimino) methyl] phenol (MPMP) followed by its extraction into a Triton X-114 surfactant-rich phase. Some important parameters affecting both complexation and extraction, such as pH, concentrations of chelating agent and surfactant, temperature, and time of equilibration, were optimized. Under optimum conditions, the preconcentration of a volume of 25 mL of sample resulted in a limit of detection of 0.21 mu g L-1, an enhancement factor of 97, and a relative standard deviation of 1.2% (n = 8, 60 mu g L-1) for the determination of Co(II) by FI-FAAS. This procedure was successfully applied to water, vitamin B-12 and B-complex samples. The accuracy was assessed employing addition-recovery experiments, independent analysis by graphite furnace atomic absorption spectrometry and by using a certified reference material.