Open Access

Christopher W. Becher, Sarah Milne, Peter M. Kaul

• Explosives trace residues on surfaces are utilized for forensic investigations and to check suspicious objects using technical and non-technical detection procedures. Data about expected trace contaminations after the handling of explosives and how they relate to a potential chemical background help to determine requirements and limitations of detection procedures. Often swab sampling is used for the analysis of surface contaminations. A wet swab sampling procedure was optimized for PETN, TNT and ammonium nitrate. Good results were achieved using PU-foam swabs wetted with a mixture of acetonitrile/water (90/10). The swabs were subsequently solvent extracted and analysed using LC-triple-quad-MS and ion-chromatography. The swabs were applied for the determination of explosives residues in a mock-up car scenario simulating one person loading the car with explosives followed by a short car travel by the same person. As test substances an ANFO, TNT and plasticized PETN were used. Additional samples were taken from indoor installations regularly used for the training of explosive detection dogs as well as other objects and buildings close by. The surface contaminations found in the investigated scenario ranged from the ng to the µg scale. The results indicate that simple cleaning procedures might not sufficient to remove explosives contaminations in training settings for explosives detection dogs. A significant spreading of explosive traces beyond direct contact with the person handling the explosive or with the explosive itself was not observed.