Reducing the Matrix Effect in Molecular Secondary Ion Mass Spectrometry by Laser Post-Ionization

Strategies to reduce and overcome matrix effects in molecular secondary ion mass spectrometry (SIMS) are investigated using laser-based post-ionization of sputtered neutral organic molecules released under C-60(+) bombardment. Using a two component multilayer film similar to that employed in a recent VAMAS interlaboratory study, SIMS depth profiles of the protonated and deprotonated quasi-molecular ions of two well-studied organic molecules, Irganox 1010 and Irganox 1098, were measured along with that of the corresponding neutral precursor molecules. When compared to composition-dependent ionization probability changes of the secondary ions, the resulting profiles are much improved. We demonstrate that detection of neutral molecules via laser post-ionization yields significantly reduced matrix effects when compared to SIMS depth profiles in both positive and negative secondary ion mode. These results suggest that this approach may provide a useful pathway for acquiring depth profiles from complex organic samples with improved capabilities for quantitation.