Adsorption studies of carbowax coated surface acoustic wave (SAW) sensor for 2,4-dinitro toluene (DNT) vapour detection

The trinitro toluene (TNT) based land mines contain 2,4-DNT as a manufacturing impurity, form more vapour in the vicinity than TNT itself, and hence, due to high vapour pressure, form a distinctive ‘chemical signature’ indicative of a land mine. The concentration of these compounds in the air over land mines is extremely low (sub-ppb level), well below the minimum detection limits of most field-portable chemical sensors, and hence detection by vapour sensing is very difficult. This paper describes the development of a polymer coated surface acoustic wave (SAW) sensor for the detection of buried/hidden explosives. For this purpose, as the first step, isotherm adsorption studies using polymer coated solid support were carried out to assess the sensitivity and selectivity of the polymer compound selected as the most suitable chemical interface in the sensor assembly. The sensor assembly was calibrated in the laboratory using 2,4-DNT vapour generated in a standardised vapour generation unit. The results indicated that the carbowax-1000 had a very good chemical interface for detection of low levels of chemical signature of explosive material. Response observed during this study was in the range of 0.56–1.1 Hz/ppb of 2,4-DNT in the laboratory condition.