Plasticizers, anti-oxidants, extenders, and other compounding ingredients migrate in plastic components, altering the physical and chemical properties of these materials. While the average bulk chemical composition may remain invariant, the spatial distribution of phases can result in local inhomogeneities and/or in compositional gradients. The analysis of these compositional gradients is made possible by spatially-resolved infrared microprobe analysis. Cross-sections of plasticized polymers were analyzed to demonstrate this technique. The factors affecting the detection and resolution of compositional gradients by spatially-resolved spectroscopy are sample geometry, spectral properties, step resolution, analytical methodology, and instrumental parameters; these factors are reviewed.