Dynamic Focusing: A New Technique for Focusing VVOC’s and Managing Water in Automated Ambient Air Analysis Using TD-GCMS

Air Monitoring, Methods, and Technology
Oral Presentation

Prepared by K. Thaxton1, J. Whitecavage2, A. Hoffmann1, L. Nünemann1, M. Haferkamp1
1 - GERSTEL GmbH, 1 Eberhard Gerstel Platz, Muelheim an der Ruhr, -- Please Select --, 45473, Germany
2 - GERSTEL Inc., 701 Digital Drive Suite J, Linthicum Heights, MD, 21090, United States

Contact Information: [email protected]; +14438334458


The determination of very volatile organic compounds (VVOC’s) becomes increasingly difficult with rising volatility. For low boiling compounds a strong sorbent is necessary for trapping and focusing, but the disadvantage of these sorbents is that they are hydrophilic. Low or cryogenic temperatures can be used for trapping and focusing, but they also do not solve the water management problem either. Therefore, a solution for effective water management is needed that doesn’t depend on either using strong, hydrophilic sorbents or trapping/focusing temperatures < 0 °C.

By using a technique developed at GERSTEL called Dynamic Focusing, very light VVOC’s like propylene and chloromethane can be trapped effectively at +10 °C using a single relatively hydrophobic sorbent. The higher temperature prevents water from freezing in the trap, and a single, relatively hydrophobic sorbent reduces the amount of water trapped.

By using Dynamic Focusing, the system can produce results that are compliant with air methods such as TO-17 and ISO 16000-6. The technique is also both cryogen free and valve free. The single sorbent is forward-flushed, without the need for backflushing or an additional conditioning step due to the omission of molecular sieve-based sorbents. The valve-less nature of the process reduces carryover, contamination, and expenses associated with regular valve replacement. Additionally there are no Teflon-based valves or other components in the sample pathway, further reducing the risk of false positives or false negatives for PFAS and related analyses.

The theory and mechanism of Dynamic Focusing will be discussed in comparison to traditional 2-stage processes (‘static focusing’). Examples based the analysis of VVOC’s and VOC’s in atmospheres will be presented, as well as analytical figures of merit (including those from a recent successful round-robin test using Dynamic Focusing).