Reduction of mass bias and matrix effects in inductively coupled plasma mass spectrometry with a supplemental electron source in a negative extraction lens

Electrons from a heated tungsten filament are created inside the extraction lens and driven out toward the skimmer. These electrons move through the ion path and reduce space charge effects between positive ions in the beam. The ion transmission efficiency is improved by factors of two (for Pb+) to 27 (for Li+). The greater sensitivity improvement for low-mass ions leads to a substantial reduction in mass bias. With the additional electrons, MO+/M+ and M2+/M+ abundance ratios increase but can be minimized with a small reduction in aerosol gas now rate. No new background ions are observed with this technique. Matrix effects can be significantly diminished when the electron source is operated under the high electron current mode. The mass dependence of matrix-induced suppression of analyte signals is essentially eliminated. Using now injection analysis to minimize solid deposition, the technique can tolerate Na matrix up to 10 000 ppm (1%) with only similar to 15% loss of analyte sensitivity.