Improvement of abundance sensitivity in a quadrupole-based ICP-MS instrument with a hexapole collision cell{

First published as an Advance Article on the web 3rd July 2002 High isotopic abundance sensitivity is desirable for the measurement of low-abundance isotopes in the presence of neighboring high-abundance isotopes. This is of interest when analyzing ultra low concentrations of trace elements or isotopes in the presence of elements or isotopes with much higher concentrations (e.g., radionuclides included in a matrix of stable isotopes). In this study, a quadrupole-based inductively coupled plasma mass spectrometer with a hexapole collision cell (ICP-CC-QMS), Platform ICP (Micromass UK), was used to study the improvement of abundance sensitivity using uranium and lutetium as examples. The median kinetic energy of 238U1 ions was about 1.2 eV and 0.9 eV when helium was introduced as a collision gas at flow rates of 5 ml min21 and 10 ml min21, respectively. In the latter case, the proportion of ions with relatively high energy decreased significantly, which improved both the transmission of ions through the hexapole collision cell and mass selection by the quadrupole mass spectrometer. When introducing helium into the collision cell a reduction in peak tail of high-abundance isotopes by up to three orders of magnitude, depending on the mass analyzed, was observed. The abundance sensitivity for 236U/238U isotope ratio was improved fro