Using a switchable-hydrophilicity solvent for the extraction−spectrophotometric determination of nickel

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A procedure was developed for the extraction and preconcentration of nickel as its dimethylglyoxime complex using triethylamine. Triethylamine on exposure to CO₂ changes its hydrophilicity and converts into a polar water-miscible form. The separation of the extractant was achieved by adding a concentrated alkaline solution to the extraction mixture. The nickel-enriched triethylamine extract was separated and evaporated, the residue was dissolved in chloroform (50 μL), and absorbance at 380 nm was measured. Conditions for the determination of nickel (pH of the medium, concentrations of dimethylglyoxime and NaOH, type and volume of dispersive solvent, ultrasonic exposure, stirring time) were optimized. A procedure for the spectrophotometric determination of nickel with a limit of detection of 0.020 μg/mL (n = 10; P = 0.95) was developed. The linearity range was from 0.050 to 0.60 μg/mL. Most of nickel-related ions (Fe³⁺, Fe²⁺, Co²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Hg²⁺) do not interfere with its determination. The procedure was applied to the analysis of water samples.