Arc-Induced Nitrate Reagent Ion for Analysis of Trace Explosives on Surfaces Using Atmospheric Pressure Arc Desorption/Ionization Mass Spectrometry.

This study presents the rapid surface detection of explosives by employing atmospheric pressure arc desorption/ionization mass spectrometry (APADI-MS) using point-to-plane arc discharge. In APADI, neutral explosives readily bind to the gas-phase nitrate ion, NO, induced by arc discharge to form anionic adducts [M+NO]. This avoids the need for inorganic anionic additives such as NO, NO, Cl, acetate, and trifluoroacetate for unique explosive ionization pathways and simplifies mass spectra. The analytical performance of APADI was thoroughly evaluated for the rapid detection of 10 explosives at levels in the range of 800 fg-1 μg. Arc-induced nitrogen oxide anions promoted the formation of characteristic adducts, such as [M+NO], and improved the instrument response for all the explosives tested. APADI showed considerable sensitivity in the negative ion mode with limits of detection in the low picogram range, particularly when explosives were analyzed on a copper or aluminum foil substrate. APADI coupled with an Orbitrap mass spectrometer displayed a good linear response for the studied explosives. The linearity and intraday and interday precisions were evaluated, demonstrating the feasibility and robustness of APADI-MS for the detection of trace explosives on solid surfaces. The mechanisms of APADI for explosive ionization and desorption were examined and verified by performing density functional theory calculations.