Automated Approach for Determination of BTEX in Soil

Importance of the Topic

The accurate measurement of volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene and xylenes (BTEX) in soil is critical for environmental monitoring, pollution assessment and risk management. Contamination from petrol leaks and underground storage tanks poses health and ecological risks, making robust, reproducible and automated analytical workflows essential for laboratories working in environmental analysis.

Objectives and Study Overview

This application note describes an automated workflow for the determination of BTEX in soil. The main goals were to develop a reliable methanolic extraction method, integrate sample preparation with headspace analysis, and demonstrate linearity, precision and recovery across a range of concentrations from low ppb to ppm levels.

Methodology and Instrumentation

A 3 g soil aliquot was weighed into a 10 ml vial, mixed with methanol and spiked with BTEX standards at six levels (66 ppb–1.7 ppm) plus a low-level 3 ppb spike. A deuterated benzene/toluene mixture served as internal standard. The automated system comprised:

• Dual-head GERSTEL MPS 2 sampler with headspace agitator
• GERSTEL mVorx vortex mixer
• Anatune CF200 centrifuge
• Agilent 7890 GC coupled to a 5977 single quadrupole MS
• Maestro software for integration

Samples were vortexed at 3000 rpm, centrifuged at 4500 rpm, and the clear supernatant diluted with a saturated salt solution for headspace sampling via a heated syringe.

Results and Discussion

SIM chromatograms showed clear detection of each analyte at 3 ppb. Six-point calibration curves for BTEX exhibited excellent linearity (r2 ≥ 0.9984). Precision studies at 333 ppb across five soil samples yielded recoveries between 82 % and 105 % and RSD of 9.5 % for benzene. Salt dilution enhanced headspace partitioning, improving repeatability. Automation with the “Prep Ahead” feature reduced total analysis time for 14 samples from over 7.5 hours to under 3 hours.

Benefits and Practical Applications

This method offers:

• Improved throughput via integrated mixing, centrifugation and HS-GC-MS
• Robust recoveries and reproducibility across diverse soil samples
• Reduced manual handling and associated contamination risks
• Scalability for routine environmental monitoring or remediation studies

Future Trends and Potential Applications

Future work may explore adaptation to clay, sand and industrial waste matrices, expand to additional VOC classes, and integrate direct coupling to high-resolution MS for non-target screening. Advances in robotic sample handlers and real-time data processing will continue to accelerate environmental analysis.

Conclusion

The automated methanolic extraction and headspace GC-MS workflow delivers a fast, sensitive and precise solution for BTEX determination in soil. The approach enhances laboratory efficiency and supports regulatory and research needs in environmental chemistry.

Reference

[1] Hewitt A.D. Comparison of Sample Preparation Methods for the Analysis of Volatile Organic Compounds in Soil Samples: Solvent Extraction vs Vapour Partitioning; Environ. Sci. Technol. 1998, 32, 143–149.