Qualitative and Quantitative Analysis of 6 Organic Explosives in Explosive Residue by Ultra-High Performance Liquid Chromatography- Quadrupole/Electrostatic Field Orbitrap Mass Spectometry

The explosive residue on the test material was wiped with a cotton ball soaked in 50% (volume fraction) acetone solution, and 5 mL of acetone was added for ultrasonic extraction for 1 min. After centrifuging for 5 min, the supernatant was volatilized to less than 0.2 mL at room temperature. The solution obtained was diluted to 1 mL with methanol, and passed through a 0.22 μm organic phase filtration membrane. The filtrate was introduced into ultra-high performance liquid chromatography-quadrupole/electrostatic field orbitrap mass spectrometer, and 6 organic explosives including trinitrotoluene (TNT), nitroglycerin (NG), taan (PETN), octogin (HMX), hexogen (RDX) and tequel (CE) were qualitatively and quantitatively analyzed according to the optimized instrument working conditions. Gradient elution was performed on ACQUITY UPLC HSS T₃ column as stationary phase with mixed solutions consisted of acetonitrile-methanol mixed solution at volume ratio of 1∶1 and 5.0 mmol·L^-1 ammonium formate solution containing 0.5 mmol·L^-1 ammonium chloride at various volume ratios as mobile phase. After ionization with atmospheric pressure chemical ionization (APCI) source, a screening list containing the exact mass number of parent ions, the exact mass number of secondary fragment ions and retention time was established by Full MS/ddMS² mode, which was used for rapid screening and confirmation of the 6 targets. The parent ions obtained from the full scan were used as quantitative ions, and quantitative analysis was made by external standard method. It was shown that corresponding peak areas of the 6 organic explosives were linearly related with mass concentrations in the ranges of 10.0-1 000 μg·L^-1 (TNT, NG, HMX and RDX) and 20.0-2 000 μg·L^-1 (NG and PETN), with detection limits of 5.0 μg·L^-1 (TNT), 8.0 μg·L^-1 (CE, HMX and RDX) and 15.0 μg·L^-1 (NG and PETN). The spiked recovery test was made on the blank cotton ball at 3 concentration levels, giving recoveries in the range of 56.6%-117%, and RSDs (n=6) of the determined values ranged from 0.40% to 6.9 %. The proposed method was applied to analysis of a real case, and TNT was qualitatively screened out.