Ultra-sensitive spectrophotometric determination of nickel after complexation and membrane filtration

We report on a simple, sensitive and selective method for the spectrophotometric determination of Ni²⁺ in water samples. The analyte ions were collected on a membrane filter in the form of their red complex with 1-(2-pyridylazo)-2-naphthol (PAN), and the absorption spectra of the colored membrane filters were acquired. Effects of pH value, sample volume, and amount of PAN were examined in order to optimize sensitivity. The interference by common other ions was eliminated using appropriate masking agents. The absorbance is linearly related to the concentration of Ni²⁺ in the ranges from 0.3 to 1.5 μg L^?1, and from 2 to 10 μg L^?1, respectively, the correlation coefficients (R²) being 0.9871 and 0.9954. Under the optimal conditions, the detection limit is 0.1 μg L^?1. The recoveries in case of spiked samples are between 95.0% and 101.5%, and the relative standard deviations range from 2.8% to 4.1%.