ISOTOPE RATIO MEASUREMENTS WITH ELEMENTAL-MODE ELECTROSPRAY MASS SPECTROMETRY

摘要

The isotope ratio capabilities of an electrospray ionization source interfaced to a quadrupole mass spectrometer are described. With the instrument operated in the metal ion mode, isotope measurements of Ag, Tl, and Pb are conducted using elemental ions produced from 1 x 10(-4) M solutions of metal nitrates or acetates in methanol. For Ag and Tl, spray conditions are identified that produce spectra free of MH(+) ions. Unbiased Ag and Tl ratio measurements with precisions of similar to 0.2% RSD are readily attained. Further improvement in relative precision appears to be limited by temporal drift in the degree of mass discrimination imparted to the measurements by the mass spectrometer. Isotopic analysis of Pb is greatly complicated by significant yields of PbH+ polyatomic ions.