Detection of multiclass explosives and related compounds in soil and water by liquid chromatography-dielectric barrier discharge ionization-mass spectrometry
In this work, the multiclass detection of explosives and related compounds has been studied by liquid chromatography-high-resolution mass spectrometry by means of a time-of-flight mass spectrometer (TOFMS) operated in the negative ion mode, using dielectric barrier discharge ionization (DBDI). Reversed-phase high-performance liquid chromatography (HPLC) separation was performed using water–methanol mobile phase without any modifier, although the effect of ammonium acetate was studied. DBD plasma was generated by applying a square wave voltage of 2.5 kV to a 100-mL min−1 He flow. The DBDI probe was adjusted to fit the commercial API source housing so that the HPLC eluent was nebulized and vaporized in the same manner as for atmospheric-pressure chemical ionization (APCI). The ionization process was affected by the temperature of the two nitrogen streams used to vaporize the solvent and the analytes, particularly for RDX and HMX, which are thermolabile compounds. The best approach in terms of sensitivity for all the studied compounds was the use of a gradient of temperatures in the ionization source, starting at 225/200 °C (vaporizer/drying gas temp) for nitramines and ending at 350/325 °C for nitroaromatic compounds. High-resolution full-scan spectra of individual selected compounds were recorded by LC-DBDI-TOFMS, and the results were compared to LC-APCI-TOFMS. A better sensitivity (slope of calibration curve) was obtained by DBDI for more than 70% of the studied compounds in both wastewater and soil extracts.
KeywordsExplosives Mass spectrometry Plasma Dielectric barrier discharge Ionization Liquid chromatography
This research received funding from the Spanish Ministerio de Economía y Competitividad (MINECO) through the project refs. CTQ-2012-34297 and CTQ-2015-71321-P and from Junta de Andalucía (project ref. FQM-2242). D.M.G. received a “Juan de la Cierva Formación” postdoctoral contract from the Spanish MINECO (ref. FJCI-2014–19573). B.G.L. received funding from University of Jaen (“Acción 6,” ref. R06/08/2018) and DAAD Re-invitation Programme for Former Scholarship Holders (ref. 91712817).
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Conflict of interest
The authors declare that they have no conflict of interest.
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