Especiação química de arsênio em samambaia utilizando espectrometria de massas com ionização ambiente

Abstract

The various chemical forms of arsenic compounds, including organic and inorganic species, exhibit different toxicities and environmental impacts. Ambient ionization mass spectrometry, such as DESI-MS (desorption electrospray ionization mass spectrometry), DESI-MSI (desorption electrospray ionization mass spectrometry imaging) and PS-MS (paper spray mass spectrometry), are excellent techniques for in situ analysis, under atmospheric pressure, at room temperature and low sample-consumption analysis to be performed with minimal sample pretreatment. These three techniques were applied for the rapid detection of inorganic compounds (arsenate - As (V) and arsenite - As (III)) and organic compounds (dimethylarsinic acid - DMA and disodium hexahydrate metilarsenate - MMA) of arsenic in fern leaves, aiming to expand applications for these techniques. Operating conditions of DESI-MS were optimized with DMA standard solution deposited on a paper surface to improve ionization efficiency. DESI-MS was applied to the fern leaves analysis artificially contaminated with As. Analyses in DESI-MSI were performed by the indirect method where the impression of fern leaf on a PTFE filter surface was made and the ions analyzed in the full scan mode. For PS-MS, fern leaf extract in methanol was placed in a triangular paper and analyzed. Mass spectra for all species of As were acquired in positive and negative ion mode and can confirm the presence of As (V) by ions of m/z 140,92, 142,93 e 160,94; As (III), by ions of m/z 106,91, 124,92, 126,94 e 144,95; DMA, by ions of m/z 138,97 e 156,98; and MMA, by ions of m/z 138,93, 140,95 e 158,96. For DESI-MS and PS-MS, MS/MS spectra were confirmed the identity of each As compound by the characteristic fragmentation profile. For the DESI-MSI, the confirmation was made by the mass error for each analyzed ion. The quantification of the As compounds by LC-ICP-MS confirmed the results obtined by three tecniques. Thus, it is possible demonstrate the applicability of the DESI-MS, DESI-MSI e PSMS as rapid, simple, efficient and with little sample preparation for detecting arsenic compounds in complex matrices.