Semi-quantitative analysis of samples in solutions using Aerodynamic Breakup Droplet ionization (ABDI) mass spectrometry

In Aerodynamic Breakup Droplet ionization (ABDI) mass spectrometry the dimer/monomer (I-2/I-1) and trimer/dimer (I-3/I-2) ratios are considered for compounds ionized in various ways. The following test compounds were selected: morphine (gives protonated ion, (M + H)(+)); hexogen, RDX (forms adducts with anion of chlorine or nitrate ion); and trinitrotoluene, TNT (gives deprotonated ion, (M-H)(center dot)). The test compounds were dissolved in water, acetonitrile or ethanol. It is shown that in the ABDI mass spectra of a number of compounds (protonated morphine ions in water and RDX adducts with chlorine in acetonitrile), the ratios I-2/I-1 and I-3/I-2 linearly depend on the analyte concentration in the solution. This is evident throughout the range of measured concentrations, when monomers and dimers are simultaneously visible in the mass spectrum. The phenomenon can be roughly explained by the dimerization of analyte molecules in singly charged parent drops during ABDI ionization. The linearity of the I-2/I-1 and I-3/I-2 on the concentration can be used for estimation of the analyte concentration in a sample without using an internal or external standard. This can be useful for routine analysis when standards are not commercially available or very expensive.