Spectrophotometric determination of cobalt, nickel and iridium after coprecipitation of their tetrahydrofurfurylxanthates on to microcrystalline naphthalene

Abstract

Cobalt, nickel and iridium react with potassium tetrahydrofurfurylxanthate to form water-insoluble, thermally stable coloured complexes. These complexes were easily coprecipitated on to microcrystalline naphthalene at pH 2.2–9.5 for cobalt, 3.7–8.6 for nickel and 6.5–9.5 for iridium and their absorption spectra showed maxima at 350–355 nm for cobalt, 415–420 and 480 nm for nickel and 380–387 nm for iridium. Beer's law was obeyed and in the concentration ranges 0–30 µg for cobalt, 10–80 µg for nickel and 35–230 µg for iridium per 10 ml of the final chloroform solution. The molar absorptivities and Sandell's sensitivities were 1.650 × 10⁴ l mol^–1 cm^–1 and 0.004 µg cm^–2 for cobalt, 3.196 × 10³ l mol^–1 cm^–1 and 0.018 µg cm^–2 for nickel and 5.013 × 10³ l mol^–1 cm^–1 and 0.038 µg cm^–2 for iridium. Ten replicate analyses of solutions containing 12.5 µg of cobalt, 45 µg of nickel and 115 µg of iridium gave mean absorbances of 0.350, 0.245 and 0.300 with relative standard deviations of 0.53, 0.47 and 0.26%, respectively. The interferences of various ions were studied and conditions were developed for the determination of these metals in certain alloys and synthetic mixtures.