Determination of Trace Amounts of Cobalt by Flame Atomic Absorption Spectrometry after Solid-Liquid Extraction and Preconcentration with Use of Nitroso-R Salt

Abstract

Cobalt was quantitatively retained by disodium 1-nittoso-2-
naphthol-3,6-disulfonate (nitroso-R salt) and tetradecyldimethylbenzylammonium
chloride on microcrystalline naphthalene in the
pH range 3.6-8.2 from large volumes of aqueous Solutions of various
alloys and biological samples. After filtration, a solid mass
consisting of the cobalt complex and naphthalene was dissolved
with 5 mL of dimethylformamide and the metal was determined by
flame atomic absorption spectrometry (FAAS). The cobalt complex
could alternatively be quantitatively adsorbed on tetradecyldimethylbenzylammonium-
naphthalene adsorbent packed in a column
and determined similarly. In this case, 0.50  μg of cobalt can
be concentrated in a column from 500 mL of aqueous sample, where
its concentration is as low as 1.0 ppb. Eight repliate determinations
of 1.0 ppm of cobalt gave a mean absorbance of 0.050 with a relative
standard deviation of 1.9%. The sensitivity for 1% absorption was
88 ppb. Various parameters, such as the effect of the pH, the volume
of the aqueous phase and the interference of a number of metal ions
on the determination of cobalt, have been studied in detail to optimize
the conditions for the determination of cobalt in various alloys
and biological samples.