Rapid preconcentration and determination of Co (II) ions in aqueous medium using ultrasound assisted cloud point extraction method

A flame atomic absorption spectrophotometric technique was studied for the preconcentration and determination of of Co2+ ions in trace amounts after ultrasound enhanced enrichment of its 1-(2-pyridylazo)-2-naphthol (PAN) complexes by cloud point extraction. The Co2+ ions were firstly complexed with PAN molecules at pH 4 and the complex transferred to a surfactant (Tergitol NP-7) rich phase with a very small volume under ultrasound waves. The surfactant rich phase was separated and dissolved by 1 mL, 1.0 M HNO3 in ethanol prior to determination of Co2+ concentration by flame atomic absorption spectrophotometry. The optimization steps of ultrasound interaction time, solution pH and surfactant volumes were achieved by response surface methodology (RSM) which is a combination of statistical approaches. Sample volume, PAN concentration and and possible interfering ions were optimized conventionally. The Co2+ ions were extracted only in 150 s at pH 4 quantitatively under optimum conditions (˃95%). The accuracy and validity of developed UA-CPE was granted by employing a certified reference material wastewater UME CRM 1204. The technique was applied to wastewater and natural water with satisfactory results.