Determination of Cobalt in Water by Thermal Lens Spectrometry with Cloud Point Extraction

A novel method is reported for the determination of cobalt using thermal lens spectrometry with cloud point extraction using 2-(3,5-dichloro-2-pyridylazo)-5-dimethylaminoaniline as the chelating agent and octylphenoxypolyethoxyethanol (Triton X-114) as the extractant. Optimized conditions for cloud point extraction included a pH of 5.0 in acetic acid/sodium acetate buffer, 4.0x10(-6) molar of the chelating agent, 0.08 percent Triton X-114 (w/v), and equilibration for twenty minutes at 60 degrees Celsius. After separation, the surfactant-rich phase was dissolved in 0.45 milliliter of 2 molar HCl-ethanol for determination. A single mode helium:neon laser at 632.8 nanometers was used for excitation and as the probe. Using the optimized conditions, a linear calibration curve was obtained from 0.2 to 4 nanograms per milliliter cobalt and the limit of detection was 0.02 nanogram per milliliter. The sensitivity was enhanced by approximately 500-fold compared to conventional spectrophotometry. The method was used for the determination of cobalt in water.