Determination of trace copper in biological and environmental samples by third derivative spectrophotometry after pre-concentration with the ion pair of nitroso-R and tetradecyldimethylbenzylammonium chloride on microcrystalline naphthalene

Abstract

Copper was pre-concentrated from a large volume of its aqueous solutions using disodium 1-nitroso-2-naphthol-3,6-disulphonate (nitroso-R salt) and tetradecyldimethylbenzylammonium chloride (TDBA +Cl −) on microcrystalline naphthalene in the pH range 5.5–7.8. After filtration, the solid mass consisting of the copper complex and naphthalene was dissolved in 5 ml of dimethylformamide and the metal was determined by third derivative spectrophotometry. Copper may also be pre-concentrated by passing the aqueous solution under similar conditions through tetradecyldimethylbenzylammonium naphthalene adsorbent packed in a column at a flow rate of 0.5–5 ml min −1 and determined similarly. The detection limit is 35 ng ml −1 (signal-to-noise ratio = 2) and the calibration graph is linear for 0.05–13 μg ml −1 Cu in dimethylformamide solution with a correlation coefficient of 0.9994 ( n = 6) by measuring the d 3A/dλ 3 between λ 1 (550 nm) and λ 2 (517 nm). Eight replicate determinations of 2.5 μg of copper in 5 ml dimethylformamide solution gave a relative standard deviation of ±1.2%. Various parameters such as the effect of pH, volume of aqueous phase and interference of a number of metal ions on the determination of copper have been studied in detail to optimize the conditions for the determination of copper in various environmental and biological samples.