Isotope Dilution-Surface Ionization Mass Spectrometry of Copper, Cadmium, and Lead in Sea Water

Abstract

Concentrations of copper, cadmium, and lead in sea water can be determined by the isotope dilution-surface ionization mass spectrometry using ⁶⁵Cu, ¹¹⁶Cd, and ²⁰⁶Pb as a triplicate spike. The fact, that Cu⁺, Cd⁺, and Pb⁺ ionic currents are emitted from the ion source of the mass spectrometer separately at different temperatures, makes possible to measure the intensity of their mass spectra, successively. After being extracted from the sea water sample into chloroform as dithizonates, three elements were treated with both nitric and perchloric acids to synthesize respective nitrates. An aliquot of aqueous solution of these nitrates was loaded onto the centre of a rhenium ionization filament and silica gel and phosphoric acid were added as stabilizers. The present method could detect the amounts of 10^-11, 10^-13∼10^-12, and 10^-13∼, 10^-12g of copper, cadmium, and lead, respectively. The effective detection limit was 10^-9, 10^-10, and 10^-10g for copper, cadmium, and lead respectively, because the sample suffered contaminations through laboratory works which amounted up to the level of 1.5. ± 0.1, 0.10 ± 0.07, and 0.3 ± 0.02 ng, again respectively. The accuracy for determinations of isotope ratios was 0.3∼2.8, 0.2∼1.9, and 0.2∼1.8% in the coefficient of variation for copper, cadmium, and lead, respectively. Replicate analyses could be performed within the error, 0.6∼8.5, 0.3∼7.5, and 0.0∼2.5% for copper, cadmium, and lead, respectively. In comparison with the method using a single spike, the present method could save analytical time, labor, expense, and the amount of important sample.