Analysis of energetic materials in various water and soil samples using HPLC and LC-MS

Importance of the Topic

Monitoring trace levels of energetic compounds in water and soil is critical for environmental protection, public safety and forensic investigations. Emerging classes of explosives such as organic peroxides and azo compounds, alongside traditional nitroaromatic and nitramine explosives, require robust analytical methods to ensure reliable detection and quantitation at regulatory limits.

Objectives and Study Overview

This study evaluates high-performance liquid chromatography with diode array detection (HPLC-DAD) and liquid chromatography-mass spectrometry (LC-MS) for the analysis of key energetic materials in environmental matrices. The method targets RCRA-listed explosives including nitrate esters (e.g., nitroglycerin, PETN), nitroaromatics (e.g., TNT, TNB, DNB isomers), nitramines (e.g., RDX, HMX) and related transformation products.

Methodology

Water and soil/sediment samples undergo salting-out extraction with acetonitrile and sodium chloride. The organic phase is isolated, back-extracted, diluted with reagent water and filtered. Separation is performed on primary reversed-phase columns (C18 or C8) with dual-wavelength detection at 254 and 210 nm. Confirmation is achieved on a secondary column (phenylhexyl or cyano chemistry) offering complementary selectivity. Sample handling employs inert, PEEK-based flow paths to minimize metal-induced artifacts. For tetryl-containing samples, acidification and acetonitrile dilution reduce rapid decomposition.

Instrumentation

• 850 Professional Ion Chromatograph (IC)
• 858 Professional Sample Processor
• 844 UV/VIS Compact IC with DAD
• Modern HPLC coupled to single-quadrupole and tandem mass spectrometers for advanced LC-MS/MS and LC-TOFMS applications

Main Results and Discussion

Quantitative separation of 15 common explosives was achieved with retention time resolution under specified conditions. Critical challenges include coelution of DNT isomers (Δ0.2 min) and tetryl instability under neutral pH and elevated temperatures. Interferences from solvents and labware were controlled via rigorous blank testing and reagent purification. LC-MS/MS offers superior sensitivity and selectivity over UV/DAD, particularly for trace-level nitroaromatics in complex matrices.

Benefits and Practical Applications

Implemented methods deliver reliable trace analysis for environmental monitoring, remediation projects, forensic investigations and regulatory compliance. The dual-detector and orthogonal confirmation approach minimizes false positives and enhances analyte identification confidence.

Future Trends and Applications

Advances in LC-MS/MS and high-resolution MS will drive further gains in sensitivity, selectivity and compound coverage. Integration of automated sample preparation, on-line solid-phase extraction and portable LC systems may enable rapid field deployable assays. Emerging data-driven workflows and machine-learning algorithms will enhance peak deconvolution and identification of novel energetic materials.

Conclusion

The combined HPLC-DAD and LC-MS workflow provides a robust platform for comprehensive analysis of diverse explosive compounds in environmental samples. Transitioning toward LC-MS/MS and advanced extraction techniques will further strengthen analytical capabilities for trace-level detection.

References

• US EPA Method 8330: Determination of nitroaromatics and nitroamines by HPLC
• Agilent Technologies 5901-7626E: HPLC analysis of explosive constituents in soil
• Agilent Technologies 5988-6342EN: Reversed-phase separation of 15 explosives from soil extract
• Agilent Technologies 5988-6345EN: Qualitative and quantitative analysis of explosives using polar and nonpolar HPLC columns
• Zhao X, Yinon J. LC-APCI-MS characterization of TNT and byproducts. J Chromatogr A. 2002;946:125–132.
• Sanchez C et al. Nitroaromatic determination at femtogram levels by C18 membrane sampling and on-line extraction with LC-MS. Anal Chem. 2003;75:4639–4645.