QUANTITATIVE CALIBRATION OF VAPOR LEVELS OF TNT, RDX, AND PETN USING A DIFFUSION GENERATOR WITH GRAVIMETRY AND ION MOBILITY SPECTROMETRY

A prototype generator for creating a continuous stream of explosive va por was referenced quantitatively both to a standard weight from the N ational Institute of Standards and Technology (NIST) and to the respon se of an ion mobility spectrometer. Vapors from solid explosive, in a precision bore glass tube at constant temperature, diffuse into an ine rt gas flow. Mass output rates were determined by (1) sample temperatu re, and (2) sample tube dimensions (length and cross-sectional area). A reference to NIST was achieved gravimetrically though a microbalance calibrated with a reference weight; mass output rates were obtained f or 2,4,6-trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX) an d pentaerythritol tetranitrate (PETN) at three or more oven temperatur es between 79 degrees C and 150 degrees C. The mass output rate was st able over hundreds of hours of continuous operation and the output was adjustable from a few picograms per second to several nanograms per s econd through variation of the oven temperature. An independent calibr ation of the vapor generator for TNT at 79 degrees C using an ion mobi lity spectrometer matched exactly the gravimetric-based findings. In m ost instances, measured mass output rates compared favorably with theo retically calculated mass output rates, with discrepancies in a few ca ses resulting primarily from uncertainties in terms (vapor pressures a nd diffusion coefficients) used to perform the calculations. Agreement is generally not good for PETN, where molecular decomposition contrib uted to higher than expected measured mass outputs. (C) 1997 Elsevier Science B.V.