Desorption electrospray ionization-high resolution mass spectrometry for the analysis of unknown materials: The phytosanitary product case.

In this work, we tested the potential of desorption electrospray ionization-high resolution mass spectrometry (DESI-HRMS) for the analysis of unknown materials. To this end, our study focused on analyzing an unknown complex sample suspected of being an adulterated phytosanitary product or a fraud. A simple and fast sample manipulation procedure (filter paper impregnated with the sample) was used for the chemical characterization of the phytosanitary product by DESI-HRMS(/MS). Kendrick Mass Defect (KMD) analysis was used to process the DESI high-resolution mass spectral data, allowing the identification of a low molecular weight polymer (polyethylene glycol) and the detection of other ions, which did not follow polymer distributions. The characteristic isotope patterns of these ions suggested the presence of organometallic compounds. Accurate mass measurements, isotope pattern fits and the structural information obtained by DESI-MS/HRMS (wide isolation window) allowed identifying the presence of triphenyltin, a biocide extensively used for agricultural purposes and restricted by the European Commission, in the phytosanitary product. The concentration of triphenyltin in the sample was 35%, which corresponds to ∼12% expressed as weight of tin, 120 times higher than the maximum legislated level.