ATOMIC ABSORPTION SPECTROPHOTOMETRIC DETERMINATION OF ZINC, CADMIUM, AND LEAD AFTER COPRECIPITATION OF THEIR MORPHOLINE-4-CARBODITHIOATES WITH MICROCRYSTALLINE NAPHTHALENE

A new method has been proposed for the atomic absorption spectrophotometric determination of zinc, cadmium and lead after coprecipitation of their morpholine-4-carbodithioate complexes with microcrystalline naphthalene. They are easily coprecipitated over the pH range, Zn:3.7-9.4, Cd:3.3-11.0 and Pb:5.4-10.2. The compound coprecipitated with solid naphthalene is separated by filtration, dissolved in 2M nitric acid and made up to 25 ml with nitric acid. The metals are determined by measuring absorbance at 213.9, 228.8 and 217.0 nm for zinc, cadmium and lead respectively. Beer's law is obeyed up to Zn:23 μg, Cd:45 μg and Pb:200 μg per 25 ml of the final solution. Ten replicate determinations of a sample solution containing, Zn:10 μg, Cd:20 μg or Pb:50 μg gave mean absorbances of 0.105, 0.095 and 0.053 with relative standard deviations of 1.42, 1.57 and 2.20% respectively. The developed method has been applied to the determination of these metals in some standard samples. Morpholine-4-carbodithioate has been used for the spectrophotometric and volumetric determination of some metal ions by a number of workers. Recently some gravimetric, thin layer and paper chromatographic separation of some metals with this reagent have been reported. In the present communication a simple atomic absorption spectrophotometric method has been developed for the determination of zinc, cadmium and lead using morpholine-4-carbodithioate as the complexing agent after coprecipitation of their complexes with microcrystalline naphthalene. The method is found to be sensitive in comparison to the extraction into molten naphthalene spectrophotometric method.