Separating VOCs From The Sample Matrix

Source: Teledyne Tekmar

Purge and Trap Background 
When using a concentrator system, it is not essential to understand how it works. However, a good grasp of the fundamentals helps you prevent problems and assists you when you are faced with tasks such as method development and troubleshooting. This section is not intended to be a full theoretical evaluation of purge and trap gas chromatography. The main purpose is to help you develop an understanding of how and why compounds are concentrated.

While gas chromatography is a very powerful analytical tool, it does have several limitations. Many different techniques have gradually developed to overcome these limitations. These techniques are for a wide variety of sample types. 

GC Detectors provide remarkable sensitivity. However, there are a number of areas where greater sensitivity is necessary. Many GC columns and detectors do not tolerate the presence of water. It may drastically reduce the lifetime of the column and adversely affect the detector performance. Gas chromatography operates as an interaction between vapor and liquid phases. The sample must start out as a vapor. For this reason, there are many samples, such as pollutants in soil or flavors in solid food, that cannot be directly introduced into a GC.

The ability to analyze volatile organic compounds is a vital part of environmental monitoring, outgassing studies, flavor or fragrance analysis, among others. Purge and Trap is a technique that separates the VOCs from a matrix. After separation, the VOCs are then concentrated and injected into the GC for separation. 

Brief History

In the 1960’s, PAT was used in the study of bodily fluids. In the mid-to-late 1970’s, PAT became a technique that was well-known and widely applied due the need to monitor VOCs in drinking water. Using this technique, it was possible to detect sup-ppb level VOCs of a wide variety. Today, PAT is routinely applied in the environmental area for the analysis of VOCs in soil and water. The arrival of microprocessor-driven systems allows the concentrator to be more precise and automated, giving the operator more time for other projects.