A simple on-site mass spectrometry method can be used to quickly detect trace quantities of triacetone triperoxide (TATP) and other explosive organic peroxides (Chem. Commun., published online Jan. 12, dx.doi.org/10.1039/b515122h). TATP (shown) is infamous for its use by the "shoe bomber" in 2001 and in the 2005 London subway and bus bombings. Terrorists favor the explosive because it's inexpensive, easily synthesized, and difficult to detect by conventional screening methods. Purdue University chemists Ismael Cotte-Rodríguez, Hao Chen, and R. Graham Cooks have now demonstrated that their recently developed desorption electrospray ionization (DESI) technique can be used to detect TATP selectively under ambient conditions without the need for sample preparation. The method, which has been used to detect TATP on paper, brick, and metal, relies on an electrospray source to generate a beam of charged microdroplets that impinge upon a sample surface. The process forms complexes of analyte molecules with alkali-metal ions that are subsequently detected.