Determination of Explosives in Soil Using the Agilent 1260 Infinity III LC System

Importance of the Topic

Explosive residues from military and civil activities can contaminate soil, posing environmental and health risks. Recent regulations in Germany require determination of specific nitroaromatic, nitramine, and nitrate ester explosives in soil, including Hexyl, which is not covered by existing methods. Reliable, sensitive analysis of these compounds is essential for environmental monitoring and regulatory compliance.

Objectives and Study Overview

This application note demonstrates a single-run LC-UV method for sixteen explosives and related compounds in soil, including the newly regulated Hexyl. It evaluates automated calibration workflows using injector-based serial dilution to streamline calibration preparation and ensure reproducible quantification.

Methodology

Soil samples were sieved and homogenized, then extracted with acetonitrile using ultrasonic extraction at 50 °C for 4 hours. After settling, extracts were filtered and spiked at 2 µg/mL. Calibration solutions (0.08–80 µg/mL) were prepared automatically by serial four-step dilution of an 80 µg/mL stock in acetonitrile with 0.1% formic acid via autosampler injector workflows. The LC method employed a pentafluorophenyl stationary phase with a gradient of 10 mM potassium phosphate buffer (pH 3) and methanol, at 0.5 mL/min flow, 25 °C, detection at multiple UV wavelengths (210–254 nm) with reference at 480 nm, and 5 µL injections.

Used Instrumentation

• Agilent 1260 Infinity III Quaternary Pump (G7111B)
• Agilent InfinityLab Assist (G7180A)
• Agilent InfinityLab Level Sensing (G7175A)
• Agilent 1260 Infinity III Vialsampler (G7129C)
• Agilent 1260 Infinity III Multicolumn Thermostat (G7116A)
• Agilent 1260 Infinity III Diode Array Detector HS (G7117C) with Max-Light 10 mm cartridge
• Agilent InfinityLab Poroshell 120 PFP column, 3.0 × 150 mm, 2.7 µm

Main Results and Discussion

Complete baseline separation of all sixteen analytes was achieved in a single 28-minute run. Retention time precision was below 0.05% RSD and peak area precision below 0.7% RSD. Calibration curves exhibited excellent linearity (R² > 0.9999) across the full concentration range, with signal-to-noise ratios at the lowest level ranging from 10 to 33. Acidic buffer conditions prevented tetryl degradation. Blank soil extracts showed no interferences, and spiked samples yielded recoveries between 91% and 102%.

Benefits and Practical Application

The combination of the PFP column and autosampler injector workflows enables single-run analysis of structurally similar isomers without manual calibration preparation. Automated dilution reduces hands-on time, minimizes operator variability, and lowers costs. The approach meets regulatory requirements and supports high-throughput environmental testing.

Future Trends and Applications

Future developments may include coupling with mass spectrometric detection for lower limits of detection, expanding the compound panel to emerging explosives, integrating in-line sample cleanup, and implementing remote monitoring with automated data analysis for field-deployable environmental screening.

Conclusion

The presented method using the Agilent 1260 Infinity III LC and Poroshell 120 PFP column offers reliable, high-resolution separation and quantification of sixteen explosives in soil. Automated calibration workflows enhance reproducibility and efficiency, making the method well-suited for environmental compliance and routine quality control laboratories.

References

• Bundes-Bodenschutz- und Altlastenverordnung vom 9. Juli 2021 (BBodSchV).
• US EPA Method 8330B Nitroaromatics, Nitramines and Nitrate Esters by HPLC (2006).
• ISO 11916-1:2013 Soil Quality – Determination of Selected Explosives by HPLC-UV.
• Agilent application note 5990-6871EN Trace Analysis of Explosives in Soil (2010).
• Agilent application note 5991-3212EN Optimizing Nitro-Aromatics Separation (2013).
• Agilent application note 5991-4373EN Positional Isomer Analysis with PFP Columns (2014).
• Agilent technical overview 5994-7703EN Automated Sample Preparation Workflows (2024).