Determination of benzene and its analogues in ambient air by an Agilent 7667A mini Thermal Desorber and an Agilent 7820A GC System

Significance of the Topic

Accurate determination of benzene and its analogues in ambient air is essential to assess air quality and meet regulatory standards such as HJ 583-2010. Thermal desorption gas chromatography coupled with FID provides a sensitive and reliable approach for trace-level volatile organic compounds monitoring in environmental and industrial settings.

Study Goals and Overview

The study aimed to validate a complete analytical solution based on Agilent technologies to quantify eight aromatic VOCs—benzene, toluene, ethylbenzene, p-xylene, m-xylene, o-xylene, styrene, isopropylbenzene—in ambient air. The method follows requirements of the Chinese standard HJ 583-2010, focusing on sensitivity, repeatability, linearity, and carryover performance.

Methodology and Instrumentation

A liquid standard series was prepared in methanol with target analytes at 5, 10, 20, 50, 100 ng per tube. The sampling used Tenax TA sorbent tubes with the following thermal desorption and GC parameters:

• Desorption: Agilent 7667A mini TD; initial 40 °C hold, ramp to 310 °C at 500 °C/min, 3 min; purge 50 mL/min for 0.5 min; bake at 320 °C for 4 min
• GC: Agilent 7820A; inlet 150 °C; nitrogen carrier at 2 mL/min; split 20:1; DB-WAXetr column (30 m×0.32 mm×1 µm); FID at 300 °C
• Oven program: 50 °C for 3 min, ramp 5 °C/min to 135 °C, hold 0 min, ramp 10 °C/min to 240 °C, hold 10 min

Main Results and Discussion

• Sensitivity: Clear separation of all eight compounds at 5 ng loading, with chromatographic peaks meeting detection requirements.
• Carryover: Secondary desorption after 100 ng injection showed no residual peaks, confirming negligible carryover.
• Repeatability: Seven replicate desorptions of 50 ng standards yielded area RSDs below 1.81% and retention time RSDs below 0.021%.
• Linearity: Calibration curves exhibited R² values ≥ 0.9992 across 5–100 ng range for all analytes.
• Real Sample Analysis: Analysis of a 4 L ambient air sample demonstrated consistent quantification without carryover.

Benefits and Practical Applications

• Compliance: Meets HJ 583-2010 standard requirements for ambient BTEX monitoring.
• Sensitivity & Robustness: Achieves trace-level detection with minimal carryover and high repeatability.
• Operational Efficiency: Automated thermal desorption eliminates solvent use and speeds sample throughput.
• Versatility: Applicable in environmental monitoring, industrial hygiene, and QA/QC laboratories.

Future Trends and Potential Uses

• Integration with mass spectrometry for enhanced compound identification at lower detection limits.
• Development of portable or field-deployable thermal desorption-GC units for on-site air monitoring.
• Expansion to broader volatile compound classes and multi-pollutant frameworks for urban air quality assessment.

Conclusion

The Agilent 7667A mini TD coupled with the 7820A GC-FID system provides a reliable, sensitive, and reproducible method for determining benzene and its analogues in ambient air. Its performance in terms of sensitivity, linearity, repeatability, and zero carryover makes it a valuable tool for routine environmental monitoring and regulatory compliance.

Instrumentation

• Agilent 7667A mini Thermal Desorber with Tenax TA tubes
• Agilent 7820A Gas Chromatograph with FID detector
• DB-WAXetr column (30 m×0.32 mm×1 µm)

References

1. HJ 583-2010 Ambient air—Determination of benzene and its analogues using sorbent adsorption thermal desorption and gas chromatography