EPA 502/524.2 VOCs using the CDS 7400 Autosampler

Importance of the topic

The analysis of volatile organic compounds in water and soil is crucial for environmental monitoring, regulatory compliance, and protection of public health. Automated purge and trap sampling improves sensitivity and throughput, enabling reliable detection of trace contaminants at parts per billion levels.

Objectives and overview of the study

This application note presents the integration of the CDS Model 7400 autosampler with the Model 7000 Purge and Trap system to perform EPA Methods 502 and 524.2 analyses. The combined system handles up to 72 samples using standard 40 ml vials, automates internal standard addition, and allows programmed sequences for replicates, blanks, and rinses.

Methodology and approach

Water samples of 5 ml volume are transferred from 40 ml vials into the purge vessel, spiked with internal standards, and purged with helium at 35 ml per minute for 11 minutes. After concentration on a trap, analytes are thermally desorbed into a gas chromatograph. The GC oven is programmed from 40 C to 220 C to resolve 63 target compounds in under 22 minutes.

Used instrumentation

• CDS 7000E Purge and Trap system with trap material Vocarb 3000
• Valve oven temperature 130 C and transfer line at 130 C
• Purge time 11 minutes, dry purge 2 minutes
• Desorb preheat at 240 C, trap desorb at 250 C for 2 minutes, trap bake at 260 C for 10 minutes
• CDS 7400 autosampler with 40 ml vial capacity, 5 ml sample loop, single rinse cycle, 2 microliters of internal standard added automatically
• Gas chromatography with helium carrier gas, split ratio 35 to 1, Rtx VMS column 30 m by 0.25 mm by 1.4 micrometers

Main results and discussion

The system successfully detected 63 volatile organics, ranging from dichlorodifluoromethane to naphthalene, at 40 parts per billion. Chromatographic separation was achieved in less than 22 minutes, illustrating the efficiency of the purge time and oven programming. Automated addition of internal standards ensured consistent quantitation and reduced manual handling variability.

Benefits and practical applications

• High sample throughput with capacity for up to 72 automated analyses
• Enhanced reproducibility and accuracy from automated internal standard addition
• Reduced operator exposure to toxic vapors and minimized manual errors
• Compliance with EPA Methods 502 and 524.2 for regulatory monitoring

Future trends and potential applications

Advances may include integration with mass spectrometry detectors for improved selectivity, miniaturized purge devices for lower sample volumes, and coupling with data analytics or machine learning for real-time decision support. Expanding the method to emerging contaminants and onsite monitoring platforms can further broaden its impact.

Conclusion

The combination of the CDS 7400 autosampler and 7000 Purge and Trap system offers a robust, automated solution for routine analysis of VOCs in water and soil. The approach delivers high sensitivity, rapid analysis times, and consistent results, addressing the needs of environmental and industrial laboratories.