Isotope dilution-surface ionization mass spectrometry of thallium, copper, cadmium and lead in purified reagents and water by sub-boiling distillation

Isotope dilution-surface ionization mass spectrometry, IDMS, using a quadri-spike solution of 203Tl, 65Cu, 116Cd and 206Pb, has been developed to determine ultra-micro amounts of thallium, copper, cadmium and lead in reagents and water purified by sub-boiling distillation. A single filament of rhenium was used as an ion source in a Hitachi RMU-6-Type Mass Spectrometer, a mixture solution of phosphoric acid and silica gel being added to a sample as a stabilizer for the ion emission. The present method has the following detection limits, Tl (10-13 -- 10-15 g), Cu (10-11 -- 10-13 g), Cd (10-12 -- 10-13 g) and Pb (10-12 -- 10-13 g), and the precision is usually better than 1% in the coefficient of variation for the determination of isotopic ratios. This means that the method can be applied to the determination of these elements at the level of ng with an effective figure of 2. This method revealed with its excellent sensitivity and accuracy that commercial high-purity reagents (HCl, HNO3, HF, HClO4, H2SO4, aq. NH3, CH3COOH and C2H5OH) and water were furthermore de-mineralized to the level of ppt by sub-boiling distillation using quartz and Teflon stills. (author)