Analytical Sciences


Abstract − Analytical Sciences, 16(5), 501 (2000).

Derivative Spectrophotometric Determination of Cobalt in Alloysand Biological Samples after Preconcentration with the Ion Pairof Disodium 1-Nitroso-2-naphthol-3,6-disulfonate andTetradecyldimethylbenzylammonium Chloride onMicrocrystalline Naphthalene or Column Method
Mohammad Ali TAHER
Department of Chemistry, Shahid Bahonar University of Kerman, Kerman, Iran
Cobalt was quantitatively retained by disodium 1-nitroso-2-naphthol-3,6-disulfonate (nitroso-R salt) andtetradecyldimethylbenzylammonium chloride (TDBA+Cl-) on microcrystalline naphthalene in the pH range 3.6 - 8.2 fromlarge volumes of aqueous solutions of various alloys and biological samples. After filtration, a solid mass consisting ofthe cobalt complex and naphthalene was dissolved with 5 ml of dimethylformamide (DMF), and the metal wasdetermined by third-derivative spectrophotometry. The cobalt complex could alternatively be quantitatively adsorbed ontetradecyldimethylbenzylammonium-naphthalene adsorbent packed in a column and determined similarly. The detectionlimit was 30 ppb (signal to noise ratio = 2) and the calibration curve was linear for 0.1 - 11 ppm in dimethylformamidesolution with a correlation coefficient of 0.9996 by measuring the distance, d3A/d rh3, between rh1 (612 nm) and rh2 (579nm). Eight replicated determinations of 2 ppm of cobalt in dimethylformamide solution gave a mean intensity (peak topeak signal between rh1 and rh2) of 0.436 with a relative standard deviation of +-0.91%. The sensitivity of the method was0.215 (d3A/dnm3) ml/g, which was found from the slope of the calibration curve. Various parameters, such as the effectof the pH, the volume of the aqueous phase and the interference of a number of metal ions on the determination of cobalthas been studied in detail to optimize the conditions for the determination cobalt in various alloys and biological samples.