Soot particles are generated from a number of sources, including auto emissions, aircraft emissions and various domestic and industrial combustor sources. Particle size and composition has been the focus of recent Environmental Protection Agency directives, especially due to the impact of small particulates on the inner urban environments. Single particle microanalysis is advantageous in these studies since, morphology and composition can be examined simultaneously. When a small sample size is available, single particle microanalysis is the only possible micro analytical approach. Chemical fingerprinting using the energy dispersive x-ray spectroscopy (EDS) signature of trace elements contained in the particles has shown remarkable source based uniqueness. Previous studies involving diesel soot particulates have indicated that most samples analyzed on a discrete basis are reasonably homogeneous, but questions still remain as to the ultimate statistical limit of this technique.