Ionization behaviors of nitrotoluenes and dinitrotoluenes by reactions with acetone‐related reactant ion

Abstract

AbstractDinitrotoluenes (DNTs) and nitrotoluenes (NTs) are found in the environment as metabolites of trinitrotoluene (TNT). When acetone is used as the solvent/eluent in atmospheric pressure chemical ionization‐mass spectrometry (APCI‐MS), the reactant ion is [2Acetone + O2]•− for the negative ion mode. The reactant ion reacts with an analyte to produce M•− and/or [M – H]− under atmospheric pressure. In this study, ionization behaviors of NT (2‐, 3‐, and 4‐NTs) and DNT isomers (2,3‐, 2,4‐, and 2,6‐DNTs) by reactions with [2Acetone + O2]•− were investigated. The energy‐minimized structures of the product ions and their energies were calculated to explain the differences in the ionization behaviors. Typical NT‐ and DNT‐related ions were produced by reactions with [2Acetone + O2]•−; NT•−, [NT – H]−, DNT•−, [DNT – H]−, and [DNT – NO]− ions. The ionization efficiencies of NT‐ and DNT‐related ions increased by increasing the source fragmentor voltage, and those of DNT‐related ions were higher than those of the NT‐related ions owing to the presence of an additional nitro group. The ionization efficiency of 3‐NT•− was higher than that of [NT – H]−, while that of [DNT – H]− was higher than those of DNT•− and [DNT – NO]−. The ionization efficiency order of NT•− was 3‐NT > 4‐NT > 2‐NT, while that of [DNT – H]− was 2,4‐DNT > 2,6‐DNT > 2,3‐DNT. The [NT – H]− and [DNT – H]− ions were stabilized by resonance structures containing nitro groups. The [DNT – NO]− ions were formed through the transition state.