Analytical Sciences

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.

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