Comparison of SIMS and MALDI for Mass Spectrometric Imaging

Abstract

Secondary ion mass spectrometry (SIMS) has become a highly refined and widely used mass spectrometric technique for the two- and three-dimensional (3D) imaging of inorganic materials, especially for the semiconductor industry. The optimization of primary ion sources for ultrahigh spatial resolution, very high transmission and high mass resolution analyzers, and specialized sample handling, particularly for wafers, has resulted in the widespread utilization of SIMS instruments for materials research and quality control in the semiconductor and magnetic materials industries. The utilization of SIMS for mass spectrometric imaging of organic and biological samples has trailed the applications for inorganic materials because of the need to improve the sub-micrometer molecular spatial resolution capabilities of SIMS that are now commonplace for inorganic and semiconductor SIMS analysis. The rapid improvements in matrix-assisted laser desorption/ionization (MALDI) for imaging macromolecular species, particularly for tissue cross sections, are now being limited by the fundamental spatial resolution capabilities of the laser desorption process. A comparison of the new developments of SIMS and MALDI instrumentation points out that these two techniques are complementary in many capabilities, especially ultimate spatial resolution and molecular mass range. An overview is presented of the SIMS process, primary ion sources, mass analyzers, and software for mass spectrometric imaging of organic and especially biological samples. Examples of the analysis of tissue cross sections, imaging resolution of subcellular features, and 3D imaging of drug delivery materials illustrate the potential for SIMS and MALDI to become invaluable complementary techniques for future mass spectrometric imaging.