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Mass spectrometry imaging (MSI) is increasingly used to produce chemical images of latent fingerprints. Yet, the actual benefits of MSI for real case studies have to be assessed for fingerprints previously processed by forensic techniques. Here, we have evaluated the compatibility of desorption electrospray ionization (DESI) with the fingerprint enhancement technique involving Oil Red O (ORO). Methods To optimize the ionization step independently from surface extraction, the ORO reagent and its mixture with model compounds (triolein and linoleic acid) were first studied in solution using high‐resolution electrospray ionization tandem mass spectrometry (ESI‐MS/MS). Then, DESI‐MSI experiments were performed in both polarity modes for ORO‐processed fingermarks deposited on pieces of paper used as porous substrates. Results ESI‐MS of ORO reveals a complex mixture of azo dyes. Two main impurities detected beside the targeted species were characterized using MS/MS and then were usefully employed to produce DESI‐MS images of fingermarks, decreasing the scanning rate to get sufficient ion abundance from natural fingerprints. ORO did not prevent chemical profiling, and one major added value of this pink dye was to produce MS images with contrast that cannot be obtained optically for some colored substrates. Conclusions DESI‐MS has demonstrated imaging compatibility with the application of ORO used to enhance latent fingerprints on paper and could also enable chemical profiling in natural fingermarks. In addition, MS images of ORO impurities were of higher quality than optical ones for fingerprints revealed on colored paper.
Banidol et al. (Thu,) studied this question.