A dual-shutter ion mobility spectrometer operating at atmospheric pressure and interfaced to a gas chromatograph for sample introduction has been used to study the reaction of Cl- with explosives. Of particular interest was an investigation of the formation of NO3- from the reaction of the Cl- with nitroglycerin (NG). The adduct NG center dot Cl- together with NO3- and NG center dot NO3- compose the mobility spectrum. Over the temperature range 111 to 122 degrees C, NG center dot NO3- is stable, but NG center dot Cl- decomposes to NO3- and 1,2-dinitro-3-chloropropane (DNClP). The activation energy and pre-exponential factor for this first order decomposition are 80 +/- 3 kJ mol(-1) and 1.3 x 10(12) s(-1), respectively. Ab initio calculation shows that the reaction is a substitution reaction occurring over a two well potential energy profile with stable ion-molecule complexes NG center dot Cl- and DNClP center dot NO3-.