Analysis of Dioxins Utilizing Time-of-Flight for Low Level Quantitation

Significance of the Topic

Dioxins rank among the most toxic persistent organic pollutants due to their stability, bioaccumulation in lipid tissues, and long biological half-life. Trace-level quantitation of the 17 toxic 2,3,7,8-chlorinated congeners is critical for environmental monitoring, food safety, and regulatory compliance under EPA method 1613B.

Objectives and Study Overview

This study evaluates the performance of an accurate-mass GC/Q-TOF system for low-level quantitation of dioxins. The goal was to demonstrate compliance with EPA 1613B criteria for chromatographic resolution, mass accuracy, mass spectral resolving power, and sensitivity.

Methodology and Instrumentation

• Sample Preparation Five-point isotope dilution calibration and continuing calibration standards were prepared following EPA 1613B guidelines. Real-world extracts were supplied by an independent laboratory.
• Gas Chromatography Agilent 7890B GC with a 60 m DB-5ms column, helium carrier gas at 1.0 mL/min, and a temperature program from 180 °C to 320 °C.
• Mass Spectrometry Agilent 7250 GC/Q-TOF system operating in electron ionization mode at 70 eV. A thermal separation probe delivered perfluorokerosene lockmass for in-run mass calibration.
• Data Processing MassHunter Qualitative and Quantitative Analysis software with the SureMass peak detection algorithm provided spectral deconvolution, accurate mass assignments, and qualifying ion ratio checks.

Main Results and Discussion

• The system delivered resolving power greater than 20 000 FWHM for all target congeners, exceeding the method requirement of 10 000 by 10% valley criteria.
• Mass accuracy remained below ±2.4 ppm across calibration levels, well within the ±5 ppm specification.
• Signal-to-noise ratios for the lowest calibration standard exceeded 10 for all analytes, confirming adequate sensitivity.
• Instrument detection limits ranged from 0.2 to 3.6 pg/mL depending on congener mass and chlorination degree.
• Real-sample analyses over a 12-hour period maintained calibration accuracy, demonstrating instrumental stability for routine workflows.

Benefits and Practical Applications

• High resolving power minimizes interferences from coeluting matrix components.
• Accurate exact mass measurements increase confidence in congener identification at trace levels.
• Time-of-flight acquisition allows full spectral recording for retrospective data mining.
• The validated method meets regulatory requirements for environmental and food safety testing, as well as contamination investigations.

Future Trends and Utilization Possibilities

• Enhanced data processing and machine learning-driven deconvolution to further improve selectivity and throughput.
• Broader adoption of GC/Q-TOF platforms in routine environmental and industrial quality control laboratories.
• Integration of automated sample extraction and cleanup to increase daily sample throughput.
• Extension of the approach to other groups of persistent organic pollutants and emerging contaminants.

Conclusion

The Agilent 7250 GC/Q-TOF platform, combined with optimized sample preparation and software-driven data analysis, meets all performance criteria of EPA method 1613B. It offers the resolving power, mass accuracy, and sensitivity necessary for reliable trace-level quantitation of dioxins.

References

• Telliard W A Method 1613B Tetra through Octa Chlorinated Dioxins and Furans by Isotope Dilution HRGC HRMS 1994
• U S Environmental Protection Agency Office of Water Method 1613B1