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Abstract
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In this research, we present a cost-effective, environmentally friendly methodology for the precise
determination of trace levels of cobalt in various environmental matrices, based on a new surfactant
micelle-mediated extraction combined with digital image analysis. Specifically, cetyltrimethylammonium
bromide (CTAB) serves as the key surfactant. Prior to extraction, the conversion of Co2+ ions into
hydrophobic species is achieved through the utilization of 1-nitroso 2-naphthol as a chelating agent. The
procedure involves injecting a tetrahydrofuran (THF) solution of CTAB into water samples containing the
target analytes and some added KI, resulting in the formation of a turbid solution due to CTAB dispersion
within the medium. Following centrifugation, the resulting precipitate is re-dissolved in 1 mL of
dimethylformamide and subjected to analysis using a self-constructed colorimeter, which is based on
a mobile device. In the colorimeter, digital image analysis is conducted using the RGB color space, with
the G channel value serving as the analytical signal. Our investigation encompasses the exploration and
optimization of several critical parameters influencing the extraction and complex formation processes.
Under optimal conditions, a linear range spanning 10–2.00 × 102 mg L−1 is achieved, exhibiting
a correlation coefficient of 0.994. The detection limit (DL) is determined to be 4.1 mg L−1. The relative
standard deviations for the determination of Co2+ at concentrations of 40 and 100 mg L−1 are found to
be 7.0 and 6.6, respectively, for five replicates. Further assessments include an evaluation of the impact
of common cations and anions on the proposed method, which subsequently qualifies it for the efficient
preconcentration and quantification of cobalt in diverse environmental matrices.
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