Identification of an Unknown Smear: Deodorant
Our laboratory was asked to identify an unknown material on a fabric. The foreign material was white in color and had a greasy consistency. We characterized the material using a variety of microscopical and instrumental techniques, including stereo and polarized light microscopy and various microchemical methods. The unknown material was a relatively complex mixture of numerous compounds. The matrix of this substance contained a combination of various hydrocarbons, but it did not suggest a specific source. We focused our investigation on some of the solid, isotropic particles that were present within the residue. We chemically analyzed these particles using both IR and Raman microspectroscopy, but they did not “match” any compounds in our substantial spectral libraries.
Elemental analysis by SEM–EDS showed that the solid particles were composed of a somewhat unusual suite of elements. We hypothesized that this component of the unknown substance could be an active ingredient commonly found in antiperspirants (aluminum zirconium tetrachlorohydrex glycine). We followed-up on this suspicion by analyzing a known antiperspirant containing the suspected active ingredient. The chemical data that we obtained from this known sample corresponded extremely well with the data previously collected from the unknown residue. This fact, combined with the general appearance and chemical composition of the unknown residue’s greasy matrix, confirmed that the unknown material on the shirt originated from an antiperspirant.