Detection of TNT in acetone using Raman spectroscopic signature

Abstract

The detection of explosive agents is becoming more important and receiving much greater emphasis for homeland defense. Raman spectroscopy is a well established tool for vibration spectroscopic analysis and can be applied to the field of explosives identification and detection. The major bands of the Raman spectroscopy of industrial TNT (Trinitrotoluene, CH₃C₆H₂(NO₂)₃) are analyzed and seven prominent peaks, that is 1616.9cm^-1 (C=C aromatic stretching vibration), 1533.9cm^-1 (NO₂ asymmetric stretching vibration), 1360.1cm^-1 (NO₂ symmetric stretching vibration ), 1210.5cm^-1 (C₆H₂-C vibration), 822.9cm^-1 (nitro-group scissoring mode), 792.3cm^-1 (C-H out-of-plane bend), and 326.7cm^-1 (framework distortion mode) are used to identify the TNT. The Raman spectroscopes of TNT solved in acetone at different mass ratios are studied, and the TNT in the solution can be detected correctly according the relative distance, intensity, and peak area of the seven peaks. The TNT prominent peaks appear clearly in high level solution (the mass ration of TNT and acetone is more than 1:10). With the decrease of TNT concentration in solution, the signature of TNT becomes more and more weak. The low detection limit of TNT is limited by the noise of the instrument (NXR FT-Raman accessory module with Nicolet 5700 FT-IR spectrometer is used for our experiments. The low detection limit in our experiments is mass ratio 1:200, which is about 4mg/mL). The prominent peak heights are discussed in consideration of the TNT concentration. Taking one of the acetone's peaks (1716.9cm^-1) as the internal standard line, the relative height of the prominent TNT peaks is almost proportional to the concentration of the TNT in the solution. A fitting curve for the relations of prominent peak height according to the concentration is proposed with multinomial fitting method, which can be used to analyze the concentration of TNT more accurately.