Transferring and optimizing the determination of explosives to fast and high resolution chromatography

Importance of the Topic

The reliable detection of trace levels of explosive residues in environmental waters is essential for assessing contamination after controlled detonations of unexploded ordnance. Monitoring nanogram concentrations of nitro-based compounds protects human health and marine ecosystems, and supports remediation efforts in coastal regions.

Objectives and Study Overview

This application note aimed to transfer and optimize a conventional explosives analysis to a fast, high-resolution liquid chromatography method. Key goals included reducing runtime, improving selectivity and sensitivity, and validating precision and linearity for eight common explosives plus an internal standard in seawater samples post-detonation.

Methodology

• Sample Preparation: 1 L seawater spiked with 5 g NaCl; enrichment on PS-DVB cartridges conditioned with methanol, acetonitrile and water; sample loading at 20 mL/min; salt wash; elution with 2×2.5 mL 50:50 methanol/acetonitrile; nitrogen evaporation at 40 °C; reconstitution in 1 mL 50:50 methanol/acetonitrile.
• Chromatographic Screening: Automated column scouting using Agilent Method Development System with seven RRHD/RRHT columns of varied chemistry; mobile phases water (A) and acetonitrile (B); linear gradient 20→95 % B over 4 min; flow 0.35 mL/min; temperature 30 °C; DAD detection at 214 nm (primary) and 235 nm (secondary).
• Calibration: Stock solutions of explosives and internal standard (2,3-DNDMB) prepared at 50 µg/mL; calibration points at 0.5–50 µg/mL with internal standard at 50 µg/mL; linearity assessed over five levels.

Instrumentation

• Agilent 1290 Infinity LC System configured with G4220A Binary Pump, G4226A Autosampler, G1316C Column Compartment, G4212A Diode Array Detector.
• C18, Phenyl-Hexyl, SB-C18, SB-AQ, SB-CN, Bonus RP, and Poroshell EC-C18 columns screened; final method used ZORBAX Stable Bond CN, 2.1×100 mm, 1.8 µm.
• Data acquisition with ChemStation C.01.01; high-precision gradient mixing via Jet Weaver; optional 60 mm high-sensitivity DAD cell for four-fold sensitivity gain.

Main Results and Discussion

• Column Scouting: Polar phases outperformed nonpolar C18; SB-CN column delivered baseline separation of eight analytes plus internal standard in 7 min.
• Performance Metrics: Retention time RSD <0.5 %; peak area RSD <1 %; resolution >2 for all critical pairs; calibration linearity R² >0.999.
• Sensitivity Enhancement: Replacing 10 mm cell with 60 mm high-sensitivity cell increased signal intensities by factor of four at 214 nm.
• Application: Detection of TNT at 8.8 ng/L in seawater after controlled detonation without matrix interference.

Benefits and Practical Applications

The optimized method delivers high throughput and robust performance for environmental monitoring and QA/QC laboratories. Short runtimes and automated column switching enable overnight method transfer and scouting. Enhanced sensitivity supports detection at sub-ng/L levels in complex matrices.

Future Trends and Applications

• Integration with high-resolution mass spectrometry for confirmatory analysis of emerging contaminants.
• Miniaturized and field-deployable LC platforms for in situ monitoring.
• Automated sample-to-result workflows combining SPE-LC-MS and advanced data analytics.
• Application expansion to soil extracts, groundwater, and industrial effluents.

Conclusion

The Agilent 1290 Infinity LC system, coupled with the ZORBAX Stable Bond CN column and optimized gradient, enables rapid and sensitive screening of nitro-explosives in seawater. Method validation demonstrated excellent precision, resolution and linearity, while the high-sensitivity DAD cell extended detection capabilities to the low-ng/L range. This approach supports environmental safety assessments and emergency response monitoring.

References

1. McCormick NG, Feeherry FE, Levenson HS. Environmental Microbiology. 176(31):949.
2. Schuster R, Gratzfeld-Huesgen A. HPLC Analysis of Explosive Constituents in Soil Samples. Agilent Application Note 12-5091-7626E, 1993.