Home > Sample Application > Thermal Desorption > Dynamic Focusing
Determination of Very-Volatile (VVOCs) to Semi-Volatile Organic Compounds (SVOCs) by TD without the need for Cryogenic Cooling 

Dynamic Focusing is a novel cryogen-free technique developed for use in thermal desorption analysis to focus and trap VOCs and SVOCs before releasing them to the GC column in a sharp band for analysis. Dynamic Focusing is the technology behind the GERSTEL TD Core System  The technique has been tested thoroughly for use with methods such as U.S. EPA TO-17 and ISO 16000-6, including successful participation in an inter-laboratory proficiency test. 

A closer look at Dynamic Focusing: 

The Dynamic Focusing technique is different from traditional thermal desorption: The trap liner is packed with a single relatively weak sorbent and the trap temperature set to +10 °C. Instead of trapping and desorbing in two separate stages, the stages are overlapped. Medium to high boilers are trapped by the sorbent and desorbed when the trap is heated. VVOCs, on the other hand, are just slowed down sufficiently by the sorbent to be focused into a sharp band resulting in  sharp peaks. The dynamic and static focusing processes are shown in the graphics below for comparison. 

The TD tube and trap are connected directly and are in-line with the GC column, reducing void volume to an absolute minimum. No valve or transfer line are needed, which would otherwise introduce active surfaces that impact analyte recovery and add moving parts that need regular maintenance causing increased cost per sample and system downtime.  No TeflonTM material is in the sample pathway, eliminating the possible introduction of PFAS-related compounds or the loss of those compounds into the PTFE.  

While ISO 16000-6 focuses on the analysis of VOCs ranging in volatility from n-C6 to n-C16, or in boiling point from 50 °C to 260 °C, US EPA TO17 includes from very volatile organic compounds (VVOCs) such as propylene (Peak #1) up to benzyl chloride (peak #25), or often to naphthalene. This is a challenging range, from a boiling point of -48 °C to 179 °C (or as high as 218 °C for naphthalene)  The compounds in a TO-17 standard are nicely separated using Dynamic Focusing as shown in the chromatogram below. 

Dynamic Focusing Benefits: 

  • Cryogen-free Peltier cooling at +10 °C focuses compounds as volatile as propylene (C3) and full range of analytes for standard air analysis methods 

  • Simplified “Direct-to Trap” design without valve or transfer line  eliminates analyte carry-over, while improving recovery and accuracy 

  • Easy to use, maintain and troubleshoot for improved uptime 

  • Inexpensive system maintenance, no valves to replace, no service calls required  

  • PTFE-free sample flow path – no PFAS degradation products or loss of PFAS  

  • Perfectly suited for: TO-17, ISO 16000-6, ASTM D-6196 

Downloads

Flyer Dynamic Focusing

Flyer TD Core