Derivative UV-visible spectrophotometric determination of nickel in alloys and biological samples after preconcentration with the ion pair of 2-nitroso-1-naphthol-4-sulfonic acid and tetradecyldimethylbenzylammonium chloride onto microcrystalline naphthal

Nickel is quantitatively retained by tetradecyldimethylbenzylammonium 2-nitroso-1-naphthol-4-sulfonate in microcrystalline naphthalene in the pH range 7.2–11.8 from a large volume of aqueous solutions of various alloys and biological samples. After filtration, the solid mass consisting of the nickel complex of 2-nitroso-1-naphthol-4-sulfonate and naphthalene was dissolved in 5 ml of dimethylformamide and the nickel as determined by first derivative UV-visible spectrophotometry. Nickel can alternatively be quantitatively adsorbed on a 2-nitroso-1-naphthol-4-sulfonic acid-tetradecyldimethylbenzylammonium-naphthalene adsorbent packed in a column and determined similarly. The detection limit is 0.3 μg ml−1 (signal to noise ratio=2) and the calibration graph is linear over the concentration range 0.9–120 μg ml−1 in dimethylformamide solution with a correlation coefficient of 0.9995 (n=6) and relative standard deviation for 8 μg ml−1 nickel of 1.4% (n=6). Various parameters such as the effect of pH, volume of aqueous phase and interference of a number of metal ions on the determination of nickel have been studied in detail to optimize the conditions for determination in standard alloys and biological samples.