Abstract
A cloud point extraction (CPE) procedure which was developed for the separation and preconcentration of trace amounts of cobalt is combined with flame atomic absorption spectrometry (FAAS) to determine trace amounts of cobalt in water and food samples. The procedure is based on the formation of the hydrophobic complex between Co(II) and 4-methoxy-2-sulfo-benzenediazoaminoazo-benzene (MOSDAA) followed by its extraction into a Triton X-114 surfactant-rich phase. The parameters such as pH of sample, concentrations of MOSDAA and Triton X-114, equilibrium temperature, and equilibrium time, which affect both complexation and extraction, are optimized. Under the selected optimum conditions, the preconcentration of 10.0 mL, 0.1 μg mL−1 Co(II) solution results in a limit of detection of 0.47 ng mL−1 (3σ) and an enrichment factor of 19. A relative standard deviation of 2.78% (, μg mL−1) for the determination of Co(II) is obtained. The proposed method was applied for the determination of trace amounts of cobalt in river water and millet samples with satisfactory results.
Highlights
Cobalt is an essential trace element in human body
It is known that the toxicity of Cobalt is quite low, but high exposure to this element can cause diseases such as asthma and skin irritation. erefore, to determine trace amounts of cobalt becomes signi cantly important in the elds of environmental analysis, process control, and medicine [2, 3]
Direct determination of cobalt ion at trace level by Flame atomic absorption spectrometry (FAAS) does not present the sensitivity requirements, and, more importantly, it is affected by matrix interference. us, preliminary separation and preconcentration of trace cobalt element from the matrix are frequently necessary to improve the detection limit and the selectivity. ese factors make several procedures developed for the separation and preconcentration of cobalt, including coprecipitation [8], liquid-liquid extraction [9, 10], solid phase extraction [11, 12], and otation [13]
Summary
Cobalt is an essential trace element in human body. Being a component of vitamin B12 (cyanocobalamin), it plays an important role in the production of the blood red cells and the prevention of pernicious anemia [1]. Cloud point extraction (CPE) has become an attractive area for the separation and preconcentration of trace metal ions [24,25,26,27]. Is method is simple experimental procedure with low cost, environmental safety, high capacity for preconcentration of wide variety of analytes, and high enrichment factor with good recoveries [28, 32, 33]. In view of these advantages, cloud point extraction and ame atomic absorption have been combined together to determine various metal ions in environmental samples [3, 34,35,36,37]. Aliquots of 15 mL of the working solution containing Co(II) ion (2.0 μμg mL−1), 0.3 mL of Triton X-114 (5.0% v/v), 1.0 mL of MOSDAA (0.02%), and 1.5 mL pH 9.0 buffer solution were mixed and placed in a graduated centrifuge tube. e mixture was diluted to 15 mL by the secondary distilled water. en, the solution was kept at 80∘C for 20 min in the thermostatic bath for equilibration. e separation into two phases was accelerated by centrifugation for 5 min at 1500 rpm. e solution was cooled in an ice bath for 10 min in order to increase the viscosity of the surfactant-rich phase and facilitate the removal of the aqueous phase. e remaining surfactant-rich phase (approximately 300 μμL) was dissolved in 0.5 mL of 0.1 mol L−1 HNO3 in order to reduce its viscosity. e Co(II) content was readily evaluated by FAAS
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