Supplementary information files for A direct analysis method using Sheath Flow Probe Electrospray Ionization-Mass Spectrometry (sfPESI-MS) to detect drug residues from forensic gel lifts

Latent fingerprints at crime scenes are frequently recovered using forensic gel-lifters, which can help to preserve the crime scene and to enhance visualization of traces such as blood or paint. In addition to providing fingerprint ridge detail, additional chemical information can also be recovered from gel lifts that may prove pertinent to an investigation. However, while DNA and metal ions have been shown to be able to be detected in gel lifted fingerprints, the determination of other types of chemical information such as the presence of drugs in gel lifted prints has not been previously shown.
This study demonstrates the application of an ambient ionisation method, sheath flow probe electrospray ionisation-mass spectrometry (sfPESI-MS) to the direct analysis of gel lifted fingerprints. A model drug compound (zolpidem) is successfully detected from gel lifted prints from 3 different surface types, glass, metal and paper. The surface activity-based separation associated with probe electrospray approaches is shown to resolve zolpidem ions from background phthalate species, significantly enhancing the response obtained from the gel-lifter. A depletion series experiment shows that the drug residue can be detected with up to 100 % efficiency after 8 consecutive contacts, however detection efficiency drops to 20 % after 30 contacts. The developed approach has potential application to analysis of historical gel-lifters to obtain additional chemical information.