Yes, we look at a lot of back-half catches. The normal approach is to first examine the residue under a microscope and see what we can determine just by looking at it. (We know this sounds terribly low tech, but you’d be amazed at what an experienced microscopist can tell just by looking.) This preliminary examination is then typically followed by either FTIR or SEM–EDS, or both. FTIR is good at identifying organic compounds in back-half catches, and we have a reference library of tens of thousands of reference spectra. It is our experience that back-half catch residues, if organic, are usually a silicone or hydrocarbon oil, but other things certainly show up. SEM-EDS analysis will result in an identification of the elements present in the residue and is most useful for inorganic compounds. The elements found generally indicate which compounds are present. In these residue samples, it is most common to find sulfates/sulfites, but again other compounds occasionally show up. In cases where the microscopist recognizes that more than one type of material is present in the residue, the materials can be isolated and each analyzed separately by the appropriate technique(s).
