Isotopenverh?ltnismessung von Mo, V, Ti und Zr sowie deren Konzentrationsbestimmung in W?ssern mit einem Thermionen-Quadrupol-Massenspektrometer

Summary Negative MoO₃^– and positive V⁺, Ti⁺, and Zr⁺ thermal ions are produced in a double-filament ion source to determine the isotope ratios of these elements in a quadrupole mass spectrometer. The average relative standard deviation for all isotope ratio measurements is 0.5%. The ratio Me⁺/MeO⁺ (Me=V, Ti, Zr) is followed dependent on the temperature of the ionization filament. A linear plot is obtained for log (Me⁺/MeO⁺) versus 1/T with increasing Me⁺/MeO⁺ ratios for higher temperatures using a single and a double-filament arrangement. An analytical procedure is developed, which allows the simultaneous measurement of Mo and V, and of Ti and Zr as well from one filament by a stepwise variation of the filament temperatures. Mo, V, Ti, and Zr traces in the ng/g and pg/g level of different water samples could be analysed with isotope dilution mass spectrometry using enriched isotopes of⁹⁷Mo,⁵⁰V,⁴⁷Ti, and⁹¹Zr. The precision lies usually in the range of 1 to 6% and the detection limits are 0.002 ng/g for Mo, 0.02 ng/g for V, 0.05 ng/g for Ti, and 0.01 ng/g for Zr using sample amounts of 250 g.