Highly Sensitive Screening Method for Nitroaromatic, Nitramine and Nitrate Ester Explosives by High Performance Liquid Chromatography—Atmospheric Pressure Ionization—Mass Spectrometry (HPLC-API-MS) in Forensic Applications

Abstract

A highly sensitive screening method based on high performance liquid chromatography atmospheric pressure ionization mass spectrometry (HPLC-API-MS) has been developed for the analysis of 21 nitroaromatic, nitramine and nitrate ester explosives, which include the explosives most commonly encountered in forensic science. Two atmospheric pressure ionization (API) methods, atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), and various experimental conditions have been applied to allow for the detection of all 21 explosive compounds. The limit of detection (LOD) in the full-scan mode has been found to be 0.012-1.2 ng on column for the screening of most explosives investigated. For nitrobenzene, an LOD of 10 ng was found with the APCI method in the negative mode. Although the detection of nitrobenzene, 2-, 3-, and 4-nitrotoluene is hindered by the difficult ionization of these compounds, we have found that by forming an adduct with glycine, LOD values in the range of 3-16 ng on column can be achieved. Compared with previous screening methods with thermospray ionization, the API method has distinct advantages, including simplicity and stability of the method applied, an extended screening range and a low detection limit for the explosives studied.

A fast liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) method for the identification of organic explosives and propellants

“…Atmospheric Pressure Chemical Ionisation (APCI) was chosen in preference to the alternative ionisation method, Electrospray Ionisation (ESI), because of the greater response for the majority of nitro-containing explosives using negative ion APCI [19][20][21]25]. Mass spectrometer settings including gas temperature, vaporiser temperature, nebuliser pressure and fragmentor voltage were then optimised for the detection of the precursor ion for analytes listed in EPA Method 8330B, and in positive ionisation for the detection of TATP.…”

“…Limits of detection (LOD) for each analyte are also included which are comparable, if not lower than current procedures using both triple quadrupole and time-offlight mass spectrometers. [18,19,25,26,38].…”

“…Current LC/MS methods have been based on the use of Electrospray (ESI) and Atmospheric Pressure Chemical Ionisation (APCI) with detection in both positive and negative modes. Negative ionisation being applicable to the analysis of nitro-containing explosives [19][20][21][22][23][24][25][26][27][28] and HME such as urea nitrate and ETN [16,29,30], with positive ionisation used for the detection of peroxide based explosives [18,[31][32][33][34], diamino nitrotoluenes [19,20] and stabilisers added to propellant formulations [22,[35][36][37].…”

Chemical Ionization Mass Spectrometry Using Carbon Nanotube Field Emission Electron Sources

“…Electron ionization (EI) and chemical ionization (CI) are both used when identifying chemical threats with MS. CI-MS is advantageous for the selective identification of explosives as they can be negatively ionized more easily than most interferents because of the strong electron affinity of the nitro group of these compounds [4]. However, gas requirements, power consumption, and inadequate lifetime are often limiting factors for the use of conventional ion sources in portable mass spectrometers.…”

Ion spectrometric detection technologies for ultra‐traces of explosives: A review

“…APCI-MS has been used for analysis of nitroaromatics, nitramines and nitrate esters explosives including the most common encountered explosives in forensic science (Xu, van de Craats, & de Bruyn, 2004a). It has been stated that APCI exhibits better limits of detection for TNT, NG, PETN ,and RDX than electrospray; with the supplementary feed of dichloromethane, the chloride adduct formation improves the sensitivity of detection by almost one order of magnitude (Evans et al, 2002).…”