Lev Gelb oral presentation (FN2-Tue2-1-3)
Incorporating Matrix Effects and Nonlinear Response in Analysis of SIMS Data
University of Texas at Dallas, 800 West Campbell Rd, TX 75082 Richardson, United States
Chemical imaging methods, including imaging mass spectrometry (MS), are increasingly used for the analysis of samples ranging from biological tissues to electronic devices. A significant barrier to wider adoption of imaging mass spectrometry is the presence of matrix effects which complicate quantitative analysis. Interactions between an analyte molecule and its surroundings (the “matrix”) can substantially alter both the yield and type of ions observed. These matrix effects result in both significant nonlinearity of signal intensity with concentration and changes in the characteristic spectrum of a given species with environment. These effects can sometimes be exploited to provide new information or increased sensitivity, as in matrix-enhanced SIMS. Quantitative analyses of matrix-affected data are rare, however, and such “intrinsic” effects can also be confused with nonlinear response due to detector saturation and other instrument-related complications.
We discuss analysis of such data using maximum a posteriori (MAP) reconstruction based on physically motivated models, and contrast this approach with statistical dimensionality-reduction techniques such as Principal Components Analysis. We present progress towards the quantitative extraction of chemical concentration profiles, component spectra, sample topography and other information from imaging mass spectrometry data in the presence of matrix effects. These include systems that demonstrate “weak” matrix effects, such as mixed self-assembled monolayers, and “strong” matrix effects such as those observed in ionic liquid matrix enhanced secondary ion mass spectrometry (Figure 1).
Figure 1. Strong matrix effects observed in ionic-liquid (IL) matrix-enhanced SIMS of a phospholipid (DPPE in MI-CHCA, from .) 3-component MAP analysis of a series of samples at varying DPPE concentration reveals significant changes in the spectra due to both IL-IL and IL-analyte interactions.
 J. J. D. Fitzgerald, P. Kunnath, A. V. Walker, Anal. Chem. 82, (2010) 4413.