The trends of individual linescans were sufficiently consistent in the 3D volume to make further analysis of compositional gradients reliable. To this end, statistical significance was pursued by classifying data points according to their distance from the center of each particle using EDM (Figure ). This choice was motivated by the hypothesis that, during synthesis, gradients are introduced as the particle grows, i.e., new compositional layers are added increasingly away from the center. Drops in the total intensity occur when material is absent, such as at the edge of the particles and in the voids that were common in the center of the secondary particles across all compositions (Figure ). The low total intensity in these regions could artificially skew the quantification of elements. Overall, evaluations of the total intensity as a function of incoming energy and relative position in the particle (Figure ) revealed that the sampling region with the highest confidence was between ~0.25 μm to ~2.0 μm from the particle surface. The most considerable drop in total intensity due to the existence of voids in the center was in the last 10-15% of the segmented data for all particles.