Benefits of Using Desorb Flow Control with the Encon Evolution

Significance of the Topic

Helium’s unique inert properties and diffusion characteristics make it the carrier gas of choice for environmental GC/MS. However, global helium shortages and costs have created an urgent need for conservation. In purge and trap methods, extended desorption times can introduce moisture into the chromatographic system, degrading calibration stability and sensitivity.

Study Objectives and Overview

This application note describes the implementation of a patented Desorb Flow Control (DFC) process on the EST Analytical Encon Evolution concentrator to meet USEPA Method 524.2 requirements. The study aims to illustrate how DFC regulates water transfer, maintains required desorb time, and substantially lowers helium use without compromising analytical performance.

Methodology and Instrumentation

Sample preparation employed a water matrix spiked with VOC standards following USEPA 524.2. The EST Encon Evolution concentrator, fitted with a Vocarb 3000 trap and Moisture Reduction Trap, was coupled to an EST Centurion WS autosampler. Desorption settings included a 4 min desorb at 250 °C with controlled pressure ramping (13.5–15 psi). GC/MS analysis used an Agilent 7890A/5975C inert XL system with a Restek Rxi-624Sil MS column (30 m×0.25 mm×1.4 µm), helium carrier, and split ratios of 40:1 (no DFC) versus 10:1 (with DFC). Calibration curves spanned 0.5–100 ppb, and selective ion monitoring of D2O (m/z 20) assessed moisture transfer control.

Main Results and Discussion

Implementation of DFC reduced desorb-phase trap flow while preserving the split ratio at the GC inlet. This adjustment lowered daily helium consumption from approximately 61.9 L to 27.4 L at a 40:1 split (80% reduction). Calibration linearity and response factors (%RSD ~1.7%) remained comparable between conventional and DFC modes. Chromatograms at 20 ppb showed equivalent analyte peaks with minimal water interference. SIM experiments with D2O confirmed effective moisture suppression during desorption.

Benefits and Practical Applications

• Helium conservation: up to 80% reduction in carrier gas use.
• Improved system stability: controlled moisture transfer prevents calibration drift.
• Maintained sensitivity: high split rates during desorb then lower split during analysis optimize detection.
• Cost savings: reduced gas consumption and maintenance downtime.

Future Trends and Potential Applications

Integration of DFC with automated sampling platforms could streamline high-throughput environmental analysis. Extending the technique to other trap materials and analyte classes may broaden its impact across food, beverage, and industrial quality control. Advances in real-time moisture monitoring and adaptive flow control algorithms promise further gains in efficiency.

Conclusion

Desorb Flow Control on the Encon Evolution concentrator offers an effective strategy for moisture management and helium conservation in purge and trap GC/MS workflows. Its ability to preserve analytical performance while dramatically reducing carrier gas usage makes it a valuable enhancement for laboratories adhering to USEPA Method 524.2 and similar protocols.

References

• US Patents 7,803,635; 7,951,609; 8,062,905 (Desorb Flow Control)
• USEPA Method 524.2, Volatile Organic Compounds in Drinking Water
• EST Analytical Encon Evolution System Documentation