FORENSICS experts will soon be able to identify drugs, gunshot residues or explosives at a crime scene in a matter of minutes, thanks to a new on-the-spot way to sample and analyse chemicals. By removing the need to take forensic samples back to the lab, it will allow detectives to understand what has happened all the quicker.
Forensic scientists currently have to take samples at a crime scene and take them back to the lab to have them analysed in a mass spectrometer. This fragments and ionises the constituent chemical components and then separates them by their mass-to-charge ratio to reveal the spectrum of atomic weights present in the sample 鈥� and hence the chemicals themselves.
To obtain their evidence, forensic scientists take swabs from the crime scene. The swabs must then be heated to vaporise the chemicals on them, or the chemicals can be dissolved off using a solvent. Although portable mass spectrometers are available, these alone are not the answer as the swabs have to be prepared in the lab.
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The new approach from Graham Cooks and his team at Purdue University in West Lafayette, Indiana, does away with swabs. Instead they fire a fine spray of charged water droplets at the surface they want to analyse. This ionises and dislodges contaminant molecules from the surface, which are then sucked up and fed into a portable mass spectrometer (Science, vol 306, p 471).
To create what they call their electrospray, the team use nitrogen gas to force water out of a capillary tube at a potential difference of around 2000 volts to the surrounding environment. At present, the system is built from standard lab equipment, but the team has patented and is developing a prototype 鈥済un鈥� that could be commercialised.
Importantly, the electrospray is safe to use on living tissue. 鈥淚t is like the mist out of a spray bottle,鈥� Cooks says, 鈥測ou can barely feel it.鈥� Indeed the team used the technique to identify an over-the-counter drug on the skin of a volunteer who had ingested the drug only 40 minutes earlier. They have also identified a variety of explosives and chemical weapons on fabric surfaces.
鈥淭he big plus here is that you can take more or less any sample to the machine with minimum preparation,鈥� comments Jim Carter, a director of Mass Spec Analytical of Bristol, UK, a forensic chemistry company.
