US EPA Method 624 with the Tekmar Lumin and the Agilent 7890B GC / 5977A MS

Importance of the Topic

The reliable detection of trace volatile organic compounds (VOCs) in wastewater is essential for environmental protection, public health and regulatory compliance. US EPA Method 624 is widely adopted by environmental laboratories, but conventional purge and trap systems can introduce excessive water vapor into gas chromatograph/mass spectrometer (GC/MS) instruments, degrading chromatographic quality and limiting sample throughput.

Objectives and Overview of the Study

This study evaluates the performance of the Teledyne Tekmar Lumin Purge and Trap (P&T) concentrator coupled with the AQUATek 100 sampler and an Agilent 7890B GC/5977A MS in accordance with US EPA Method 624. Key goals include assessing water vapor removal efficiency, calibration linearity, method detection limits (MDLs), accuracy, precision and overall cycle time reduction through elimination of dry purge.

Methodology

The experimental workflow followed US EPA Method 624 sample preparation and calibration steps:

• Preparation of calibration standards from 0.5 ppb to 200 ppb using EPA 624 Volatiles MegaMix and Calibration Mixes.
• Use of three internal standards (bromochloromethane, 2-bromochloropropane, 1,4-dichlorobutane) and three surrogate standards (pentafluorobenzene, fluorobenzene, bromofluorobenzene).
• Determination of MDL, accuracy and precision using seven replicate 0.5 ppb standards.
• Analysis under Lumin and GC/MS conditions optimized for moisture control, as detailed in the application note.

Used Instrumentation

• Teledyne Tekmar Lumin Purge and Trap concentrator with Moisture Control System (MCS).
• AQUATek 100 autosampler.
• Agilent 7890B gas chromatograph equipped with a 20 m × 0.18 mm DB-624 UI capillary column (1 µm film).
• Agilent 5977A mass selective detector operating in full-scan mode (35–260 m/z).

Key Results and Discussion

The Lumin’s MCS effectively removed water vapor without requiring any dry purge time, yielding sharp chromatographic peaks for both low- and mid-boiling VOCs. Calibration performance across 30 compounds demonstrated:

• Linearity coefficients (r2) above 0.997 for the majority of analytes.
• Relative response factor %RSD values typically below 10%, meeting method criteria.
• MDLs in the 0.03 to 0.83 ppb range, with consistent detection at 0.5 ppb levels.
• Accuracy between 89% and 118% and precision (%RSD) generally below 11% for the 0.5 ppb fortifications.

Chromatograms of a 0.5 ppb standard confirmed minimal water interference for early-eluting gases. Stability testing over nine hours for 27–30 samples showed internal and surrogate standard %RSD values typically below 4%, indicating robust system repeatability.

Benefits and Practical Applications

The integration of the Lumin P&T concentrator with the MCS allows:

• Elimination of dry purge steps, reducing sample cycle time.
• Improved chromatographic resolution for moisture-sensitive analytes.
• Enhanced laboratory throughput, enabling more samples per 12-hour period.
• Compliance with regulatory method performance criteria for calibration, MDL, accuracy and precision.

Future Trends and Opportunities

Advancements in moisture control and trap cooling are poised to further increase sensitivity and reduce analysis time. Potential developments include:

• Integration of real-time moisture monitoring at the transfer line.
• Automated optimization of trap temperature profiles for diverse compound classes.
• Adaptation of MCS technology to other purge and trap platforms for broader applicability.
• Coupling with high-resolution MS for enhanced specificity in complex matrices.

Conclusion

The Teledyne Tekmar Lumin P&T concentrator combined with the AQUATek 100 and Agilent 7890B/5977A GC/MS successfully performs US EPA Method 624 without a dry purge step. This configuration delivers excellent water vapor management, high calibration linearity, low MDLs, accurate and precise measurements, and faster cycle times, supporting improved laboratory efficiency and reliable VOC analysis in wastewater.

References

• US EPA. Method 624: Purgeables. Appendix A to Part 136—Methods for Organic Chemical Analysis of Municipal and Industrial Wastewater. Promulgated 1984.