Desorption–ionization on silicon (DIOS) is a new, matrix-free laser desorption mass spectrometry approach that allows for the direct identification of low molecular weight compounds in the presence of potentially interfering compounds. The porous silicon surfaces provide a scaffold for trapping analyte molecules, and are readily adaptable to commercial time-of-flight instruments. As an example of its utility in forensic cases, DIOS mass spectrometry was used to distinguish between similar synthetic polymers and identify specific polymers from complex biological media. Despite the absence of matrix, specific low molecular weight polymers were rapidly identified without any fragmentation. This method was applied to the rapid identification of ethoxylate polymers during a criminal investigation.