An ambient mass spectrometry (AMS) platform coupling Joule heating thermal desorption (JHTD) and direct analysis in real time (DART) was developed, generating discretely pulsed rapid heating ramps and elevated temperatures for the detection of inorganic nitrite, nitrate, chlorate, and perchlorate salts. Passing a few amperes of DC current through a nichrome wire enabled resistive heating rates and temperatures up to approximately 400 °C/s and 750 °C. JHTD expanded the utility and capabilities of traditional DART-MS for the trace detection of previously undetectable inorganic compounds. A partial factorial design of experiments (DOE) was implemented for the systematic evaluation of five system parameters. A base set of conditions was developed for JHTD-DART-MS and demonstrated sensitive detection of a range of inorganic oxidizer salts, down to single nanograms corresponding to signal-to-noise ratios in the range of 30 to 40. DOE also identified JHTD filament current and in-source collision induced dissociation (CID) energy as inducing the greatest effect on system response. Control of JHTD current provided a method for controlling the relative degrees of thermal desorption and thermal decomposition. Furthermore, in-source CID provided manipulation of adduct and cluster fragmentation, optimizing the detection of molecular anion species. Finally, the differential thermal desorption nature of the JHTD-DART platform demonstrated efficient desorption and detection of organic and inorganic explosive mixtures, with each desorbing at its respective optimal temperature.
Joule heating, direct analysis in real time, mass spectrometry, inorganic detection, fuel- oxidizer mixtures, homemade explosives, in-source collision induced dissociation