Pattern recognition based identification of nitrated explosives

Abstract

We report an effective approach for the identification of nitro explosives by the reaction of an electron-acceptor with an electron-donor with and without the addition of γ-cyclodextrin (γ-CD). A charge-transfer complex was prepared in acetonitrile by the reaction of the nitro explosive TNT as an electron acceptor with the donor N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD). The complex TNT/TMPD converts gradually into TNT˙⁻/TMPD˙⁺ in water with 5% acetonitrile by volume. The inclusion behavior of TNT˙⁻/TMPD˙⁺ with γ-CD was studied by UV-visible spectroscopy. The effect of α- and β-CD with TNT˙⁻/TMPD˙⁺ was also studied. Similar experiments were also carried out for RDX˙⁻/TMPD˙⁺ with γ-CD. The binding of TNT˙⁻/TMPD˙⁺ and RDX˙⁻/TMPD˙⁺ with γ-CD were compared for the application of the complexes in a sensor array. Subsequently, the visible absorption spectra of nitro explosives as analytes, such as TNT, RDX, HMX and Tetryl with TMPD in the presence and absence of γ-CD, were measured with time. We worked with the same analytes with a second electron donor tetrakis(dimethylamino)ethylene (TDAE) using 96-well plate experiments. Pattern recognition analysis was applied to analyze the data collected and it showed successful discrimination of the nitro explosives. This work represents the simplest colorimetric chemical sensor technique to be used in monitoring the range of common nitro explosives.