Maximizing Production While Minimizing Costs

Significance of the Topic

The demand for higher sample throughput and reduced per‐sample cost is growing in environmental laboratories. Strict regulatory requirements for volatile organic compound (VOC) analysis, such as US EPA Method 8260b, necessitate reliable purge and trap systems that manage moisture interference and maintain rapid cycle times within standard work shifts.

Study Objectives and Overview

This study evaluated a dual purge and trap configuration combining two Encon Evolution concentrators with a single EST Analytical Centurion WS autosampler and an Agilent GC/MS system. Objectives included:

• Validating calibration performance for a broad range of VOC analytes under EPA Method 8260b
• Assessing precision, accuracy, and system cleanliness over a three‐day sequence
• Demonstrating throughput gains and cost efficiencies compared to a single‐trap setup

Used Instrumentation

• EST Analytical Centurion WS autosampler
• Two Encon Evolution purge and trap concentrators equipped with Voccarb 3000 traps and Moisture Reduction Traps (MoRT)
• Agilent 6890A gas chromatograph with RTX-624 30 m×0.25 mm×1.4 µm column
• Agilent 5973 mass spectrometer (m/z 35–265 scan range)

Methodology and Instrument Parameters

Purge and Trap Conditions:

• Purge volume: 100 mL at 400 mL/min for 11 min
• MoRT temperature: 39 °C; trap bake at 265 °C
• Desorb at 260 °C with 5 psi pressure control, followed by ambient dry purge
• Sample size: 10 mL water, 5 µL internal standard

GC/MS Conditions:

• Split mode inlet at 200 °C, 40:1 ratio
• Oven program: hold 40 °C (1 min), ramp 18 °C/min to 220 °C (hold 11 min)
• Helium carrier at 1.2 mL/min; MS source 230 °C, quad 150 °C, transfer line 180 °C

Calibration and Standards:

• US EPA Method 8260b standard mix from Restek; concentration range 0.5–200 ppb
• Calibration curves for two concentrators met method criteria with R² >0.995 and %RSD <15%

Main Results and Discussion

• Calibration: Both concentrators achieved linear response across 0.5–200 ppb, satisfying EPA 8260b requirements.
• Precision and Accuracy: Triplicate 20 ppb and 50 ppb check standards over three days exhibited average recoveries within 80–120% and RSDs generally below 10% for target analytes.
• Internal Standard Stability: Daily RSDs for multiple labeled standards remained under 5% across 33 runs, confirming autosampler consistency.
• Throughput Improvement: Single‐trap systems require ~25–30 min per sample due to mandatory 11 min purge. The dual‐trap configuration reduces the limiting factor to GC/MS cycle time (~15 min), effectively doubling sample throughput without additional GC/MS hardware.

Practical Benefits and Applications

• Enhanced productivity: One analyst can process up to twice as many VOC samples within a typical 12‐hour shift.
• Lower per‐sample cost: Shared GC/MS resources and a single autosampler reduce capital and maintenance expenses.
• Improved data quality: Moisture reduction traps minimize water carryover, preserving chromatographic resolution and detector sensitivity.

Future Trends and Potential Applications

Emerging innovations may include:

• Integration of multi‐trap systems with real‐time data monitoring and automatic fault detection
• Advanced trap materials offering broader analyte ranges and faster heating cycles
• Application of artificial intelligence for predictive maintenance and optimized scheduling of sample runs
• Hybrid automation platforms combining purge/trap with other sample‐preparation techniques for expanded analyte classes

Conclusion

The dual purge and trap approach using two Encon Evolution concentrators paired with a single autosampler and GC/MS meets EPA Method 8260b performance criteria while drastically increasing sample throughput and reducing operational costs. This scalable configuration offers environmental laboratories a practical solution for high‐volume VOC monitoring.

References

• US Environmental Protection Agency, Method 8260b: Volatile Organic Compounds by Gas Chromatography/Mass Spectrometry
• Restek Corporation, Volatile Organic Compound Calibration Standards