Enhanced Analysis of explosives listed in EPA Method 8330B using APCI-LC-MS/MS

Significance of the Topic

The analysis of nitroaromatic and nitramine explosives is essential for environmental monitoring and public health protection. Residues from military, mining, and construction activities can contaminate soil and water, leading to serious health issues such as leukemia, reproductive disorders, and ocular damage. Highly sensitive and selective analytical methods are required to detect trace levels of these compounds and ensure regulatory compliance.

Objectives and Study Overview

This study aimed to enhance the EPA Method 8330B for explosives by developing two atmospheric pressure chemical ionization LC-MS/MS methods (cold and hot source configurations) on a Shimadzu LCMS-8050 system. Key goals included:

• Optimizing ionization parameters for 17 explosives and related nitroaromatic byproducts.
• Establishing MRM transitions with adequate sensitivity, linearity, and precision.
• Validating method performance in a river water matrix at environmentally relevant concentrations.

Methodology and Instrumentation

The analytical workflow combined UHPLC separation and tandem mass spectrometry:

• LC system: Shimadzu Nexera UHPLC with Shim-pack Velox SP-C18 column (2.1×100 mm, 2.7 µm).
• Mobile phase: isocratic 70% water/30% methanol at 0.4 mL/min, 30 °C column temperature.
• MS detection: Shimadzu LCMS-8050 with APCI source in two configurations:
   
  • Cold method (250 °C interface, 150 °C DL/heat block) for nitroaromatics and nitramines.
  • Hot method (500 °C interface, 300 °C DL/heat block) for compounds with lower polarity.
• MRM optimization: flow injection analysis to select precursor/product ions and collision energies for 17 target analytes.
• Calibration: standards from 0.001 to 5 µg/mL, covering LOQs down to 0.001 µg/mL and achieving R² ≥ 0.961.

Main Results and Discussion

Source temperature optimization improved sensitivity for nitrotoluenes and nitrobenzene. Two APCI methods provided optimal ionization for all targets, avoiding in-source fragmentation. Key performance metrics:

• Linear range: 0.001–5 µg/mL for most analytes; PETN and NG up to 5 µg/mL.
• Correlation coefficients (R²): ≥ 0.997 across compounds.
• LOQ %RSD: 1.6–26.9%, with most analytes < 10% RSD at lowest calibrator.
• Spike recovery in river water: consistent quantification at or near LOQs (0.001–0.05 µg/mL).

The automated switch between cold and hot methods enabled seamless analysis of the full EPA 8330 panel without instrument downtime.

Benefits and Practical Applications

This enhanced APCI-LC-MS/MS approach offers:

• Improved sensitivity and selectivity over traditional PDA detection.
• Accurate trace-level quantification of explosives in complex matrices.
• MRM-based confirmation via unique fragmentation patterns.
• Automated dual-method operation for comprehensive compound coverage.

Applications include environmental monitoring, forensic investigations, and QC in munitions manufacturing.

Future Trends and Potential Applications

Advances may include:

• Integration of high-resolution MS for broader screening of related transformation products.
• Miniaturized or field-deployable LC-MS platforms for on-site sampling.
• Coupling with automated sample preparation to increase throughput.
• Multimodal ionization sources to expand analyte scope.

Conclusion

Two optimized APCI-LC-MS/MS methods on a Shimadzu LCMS-8050 successfully quantified all 17 explosives listed in EPA Method 8330B with high sensitivity, precision, and linearity. The dual-source configuration enabled full panel coverage with minimal compromise in performance and efficient analysis of environmental water samples.

Reference

• Enhanced Analysis of explosives listed in EPA Method 8330B using APCI-LC-MS/MS, Shimadzu Scientific Instruments, application note.