Determination of Cadmium by Isotope Dilution-Surface Emission Mass Spectrometry

Abstract

A minute amount of cadmium can be determined by the isotope dilution method with surface emission mass spectrometry using ¹¹⁶Cd as a spike. After extracted into 15 ml of 0.00125% dithizone chloroform solution from the sample spiked with ¹¹⁶Cd, cadmium is back extracted into 5 ml of 7 N nitric acid. The nitric acid solution is treated with 0.1 ml of 60% perchloric acid and dried up in a heated pyrex glass oven supplied with a high purity nitrogen gas. The residue is dissolved in a mixture of 60 μl of 0.003% silica gel suspended water and 5 μl of 2% phosphoric acid. An aliquot of the dissolved solution is loaded onto the center of a rhenium single filament in a surface ionization device of the mass spectrometer. The present method can determine the ratio of ¹¹⁴Cd/¹¹⁶Cd with the precision from 0.4 to 1.1% in coefficient of variation, where the detection limit for Cd⁺ ion is 10^-14∼10^-18 g. The application of the present method to orchard leaves delivered by National Bureau of Standards, U. S. A., as a standard reference material in environments has proved its superior usefulness by giving results in close agreement with those certified by N. B. S.