Automated Detection of Selected Explosives and Related Compounds

Importance of the Topic

The presence of nitroaromatic explosives and related compounds in ground and surface waters poses a significant environmental and health risk. Legacy contamination from military sites, training grounds and former ammunition factories can persist for decades. Regulatory standards such as DIN EN ISO 22478:2006 and drinking water directives demand reliable monitoring of these highly toxic substances to ensure water safety and compliance.

Objectives and Overview of the Study

This application note describes the development and validation of a fully automated sample preparation workflow for detecting selected explosives in 1 L water samples. The primary goal was to integrate manual solid phase extraction (SPE) steps into the FREESTYLE XANA robotic system to achieve high throughput, reproducibility and conformity to established norms.

Methodology and Instrumentation

Sample Preparation and SPE

• Tap water samples spiked at 1 µg/L per analyte with added sodium chloride (5 g/L) to enhance extraction efficiency.
• Manual SPE steps: conditioning with methanol, acetonitrile and water; sample loading at 1 000 mL/h; washing; elution with methanol–acetonitrile (1:1).
• Automated SPE using FREESTYLE XANA: parallel handling of up to three 3 mL HR-X cartridges, including conditioning, loading (10 mL/min), washing, drying (air purge) and elution into vials or evaporation module.
• Eluent exchange: methanol rinse, addition of water keeper, evaporation under nitrogen at 30 °C to 0.5 mL, dilution to 1 mL.

Used Instrumentation

Automated Sample Preparation

• FREESTYLE XANA platform with SPE module, sample rack for 24 × 1 L bottles and EVAporation module for concentration.

HPLC-UV Analysis

• Shimadzu Nexera 2 system: dual pumps, autosampler, column oven, PDA detector.
• Two NUCLEOSHELL® columns (RP-18 and Phenyl-Hexyl, 150×2 mm, 2.7 µm) to resolve closely eluting isomers (e.g., TNT vs. Octogen).
• Gradient elution with water/methanol mixtures containing 25 mM ammonium acetate (pH 4); flow 0.5 mL/min; injection 25 µL; detection at 210, 230, 254 and 360 nm.

Main Results and Discussion

Recovery and Precision

• Automated SPE recoveries ranged from 77 % (DEGDN) to 99 % (TNT, Octogen) with RSDs typically below 10 %.
• Isomer separation was optimized by using Phenyl-Hexyl column for TNT and Octogen, preventing coelution.

Throughput and Reproducibility

• Unattended operation 24/7 enabled high sample throughput via parallel processing and automation.
• Results complied with DIN EN ISO 22478:2006 requirements for drinking and ground water testing.

Benefits and Practical Applications of the Method

• Significantly reduced hands-on time compared to manual SPE, freeing analysts for other tasks.
• Enhanced reproducibility and traceability through automated protocol execution.
• Scalable solution for environmental monitoring laboratories, defense sites and regulatory agencies.

Future Trends and Potential Applications

Integration of online SPE with tandem mass spectrometry could further improve sensitivity and selectivity. Expansion to emerging contaminants such as per- and polyfluoroalkyl substances (PFAS) and pharmaceutical residues is feasible by adapting cartridge chemistries and detection methods. The use of machine-learning algorithms for chromatogram evaluation may streamline data processing and anomaly detection.

Conclusion

The automated workflow on the FREESTYLE XANA platform delivers robust, high-throughput detection of explosives and related compounds in water samples. It meets regulatory standards, improves laboratory efficiency and supports continuous environmental monitoring.

References

• DIN EN ISO 22478:2006 (F21)
• German Drinking Water Ordinance (TrinkwV)
• US EPA Method 8330