Noncontact Detection of Absorbed Dinitrotoluene Using Laser Electrospray Mass Spectrometry

Noncontact detection of the explosive signature molecule 2,4-dinitrotoluene (DNT) from both metal and sand substrates using laser electrospray mass spectrometry (LEMS) is investigated. The measurement of DNT mass spectral signal intensity as a function of laser vaporization energy reveals that the optimal laser pulse energy for metal (0.4 mJ) is lower than that for dielectric substrates (1.2 mJ). The effects of laser spot area and laser power density on the LEMS analysis of DNT were studied at fixed laser pulse energies. The LEMS signal intensity of DNT is modeled as the product of laser spot area and laser power density. The model shows that both parameters contribute to the measured signal intensity, in agreement with experimental data. Furthermore, investigations of the DNT signal intensity as a function of nine different sampling tube positions were conducted to improve the capture efficiency of laser-vaporized analytes. The limit of detection (LoD) for DNT using LEMS is 15 ng through noncontact detection using a Venturi pump remote sampling system.