Dead time determination in the isotopic composition analysis of copper and zinc solutions enriched in 65Cu and 68Zn
摘要
In the isotopic composition analysis of substances and materials using a quadrupole inductively coupled plasma mass spectrometer, the main source of bias in the measured isotope ratios is the detector’s dead time. In this connection, it is important to determine the detector’s dead time when developing reference materials for isotopic composition and to correct the obtained results accordingly. The article considers three methods of dead time determination that rely on measuring the isotope ratios 63Cu/65Cu, 64Zn/68Zn, 66Zn/68Zn, 67Zn/68Zn, and 70Zn/68Zn in copper and zinc solutions with different mass fractions, as well as a method for comparing pulse and analog signals from the detector of a quadrupole inductively coupled plasma mass spectrometer. These four methods were used to study how the detector’s dead time affects isotope ratio measurements in the isotopic composition analysis of copper and zinc solutions enriched in 65Cu and 68Zn isotopes, respectively. The uncertainties of the obtained dead times were estimated using the specified methods. As a result, the most accurate methods for determining the detector’s dead time were selected: slope analysis and iterative method (Methods 3 and 4). For the solution isotopically enriched in 65Cu, the detector’s dead times obtained via Methods 3 and 4 amounted to (73±4) ns and (76±4) ns, respectively. In the case of the 68Zn isotopically enriched solution, Method 4 proved to be the most accurate, with the detector’s dead time amounting to (42±4) ns. The obtained results were used in the development and characterization of reference materials for the isotopic composition of copper and zinc solutions enriched in 65Cu and 68Zn isotopes.