When single hair reveals cocaine habit of consumption: MALDI imaging vs. LC-MSMS

The hair has the unique capacity of “trapping” psychoactive substances within it. Thus, punctual or repeated drugs exposure can be revealed during hair analysis. Matrix assisted laser desorption ionization (MALDI) of single hair offers many advantages over conventional techniques such as liquid chromatography-tandem mass spectrometry (LC-MSMS): low amount of sample, simplified sample preparation and high spatial resolution of MALDI images (∼100 μm). We present a method to characterize and localize cocaine and its metabolites, the benzoylecgonine and cocaethylene in a single hair from two chronic abusers of drugs using MALDI-QIT-TOF (Quadrupole Ion Trap-Time of Flight) mass spectrometry coupled to imaging. Few hair of two regular cocaine and alcohol users, called patients A and B were decontaminated in successive water and dichloromethane baths, then oriented and cut longitudinally using a home-made cutting device. Uniform layers of α-cyano-4-hydroxycinnamic acid (CHCA) matrix were sprayed over the hair samples using an automatic and thermo-regulated sprayer (TM-Sprayer™, HTXImaging). Acquisitions in MS/MS mode were performed according to a raster adjusted at 80 μm using a MALDI-QIT-TOF instrument (Axima Resonance, Shimadzu). MS/MS images of two hair per patients were reconstituted using the BioMap® imaging software and then processed using the Quantinetix® software. The MALDI-MS/MS images highlight, over the last four months preceding the hair collection, a decrease in cocaine quantity for patient A, while an increase is observed for the patient B. Consumption profiles are compared with those obtained by liquid chromatography-tandem mass spectrometry, considered as the gold standard and the results are well correlated with those of the reference method. A manual procedure of hair longitudinal section is introduced. The results obtained after MALDI analysis are exploited as images in MS/MS mode and demonstrates cocaine use in the four months prior to collection for both drug users. In addition, the consumption profiles are comparable with those obtained by LC-MS/MS, confirming that the MALDI imaging is a method which efficiently characterize and map cocaine and its metabolites in single hair.