Spectrophotometric and chromatographic determination of insensitive energetic materials: HNS and NTO, in the presence of sensitive nitro-explosives

Abstract

As there are no molecular spectroscopic determination methods for the most widely used insensitive energetic materials, 2,2′,4,4′,6,6′-hexanitrostilbene (HNS) and 3-nitro-1,2,4-triazole-5-one (NTO), in the presence of sensitive nitro-explosives, two novel spectrophotometric methods were developed. For HNS and TNT mixtures, both analytes react with dicyclohexylamine (DCHA) forming different colored charge-transfer complexes, which can be resolved by derivative spectroscopy. The spectrophotometric method for NTO measures the 416-nm absorbance of its yellow-colored Na+NTO− salt formed with NaOH. TNT, if present, is pre-extracted into IBMK as its Meisenheimer anion forming an ion-pair with the cationic surfactant cetyl pyridinium (CP+) in alkaline medium, whereas the unextracted NTO is determined in the aqueous phase. The molar absorptivity (ɛ, Lmol−1cm−1) and limit of quantification (LOQ, mgL−1) are as follows: for HNS, ɛ=2.75×104 and LOQ=0.48 (in admixture with TNT); for NTO, ɛ=6.83×103 and LOQ=0.73. These methods were not affected from nitramines and nitrate esters in synthetic mixtures or composite explosives. The developed methods were statistically validated against HPLC, and the existing chromatographic method was modified so as to enable NTO determination in the presence of TNT. These simple, low-cost, and versatile methods can be used in criminology, remediation/monitoring of contaminated sites, and kinetic stability modeling of munitions containing desensitized energetic materials.