Adsorption studies of carbowax and poly dimethyl siloxane to use as chemical array for nitro aromatic vapour sensing

Trinitro toluene (TNT)-based explosives contain 2,4-dinitro toluene (DNT) and 1,4-dinitro benzene (DNB) as a manufacturing impurity, which form more vapour in the vicinity than TNT itself, and hence form a distinctive 'chemical signature' indicative of explosive. The concentration of these compounds over landmines is extremely low and well below the minimum detection limits of most field-portable chemical sensors. Carbowax was found to give good adsorption for 2,4-DNT vapour at higher temperature and reverse was in case of 2,6-DNT vapour. On the other hand, the same polymer film gives reasonably good adsorption for 1,4-DNB, more than 33% adsorption and poor response for 1,3-DNB, which is around only 20%. The adsorption rate was specific for all the four isomers as observed 0.81 ng/(cm2 min) for 2,4-DNT, 0.14 ng/(cm2 min) for 1,3-DNB, 0.07 ng/(cm2 min) for 2,6-DNT, and 0.04 ng/(cm2 min) for 1,4-DNB. This polymer was found to give different relative response to these nitro aromatic isomers. PDMS gives very good response for 2,4-DNT (98-100%) at 50 °C appears to be a distinguishing performance. The results of carbowax-1000 and poly dimethyl siloxane (PDMS) indicated that these two polymers could be more suitable for the realisation of polymer-based chemical sensor.