Using a Purge and Trap Autosampler: Frequently Asked Questions

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In elemental analysis equipment, the term purge and trap refers to a type of autosampler inlet that uses a mechanism to introduce the sample. Often used for gas chromatography, inlets that feature purge and trap technology have the ability to detect compounds at low parts per billion (ppb) levels. Thus, they are the preferred type of inlet for testing for volatile organic compounds (VOCs), dangerous gases that typically vaporize at room temperature.

A purge and trap autosampler is an improvement upon autosamplers that require the sample to be injected by hand. In addition to preserving the integrity of the sample, purge and trap mechanisms also help to protect the tester and streamline the gas chromatography process. If you are considering investing in an autosampler, but you need to have some questions answered before you do, the answers below could help:

Besides VOCs, what else are purge and trap autosamplers used to analyze?

In addition to VOCs, they are often used to study soil and water in the following capacities, among others:

  • Analyzing the types of chemical pollution at brownfield sites
  • Analyzing pollutants in waste water
  • Checking for pollutants in surface water and drinking water
  • Testing crop soil for vitality
  • Testing the soil in low emissions zones (LEZ) for certain types of particulates

Autosamplers are used for commercial purposes and much as they are used for environmental purposes. They can also be used for food and beverage analysis.

What testing process does a purge and trap autosampler expose a sample to?

They put the sample through a five-part process before delivering it to the column of the gas chromatograph:

  • Bubble carrier gas through the sample
  • Purge the compounds that are being tested for
  • Hold the compounds in the concentrator
  • Vaporize the compounds by heating the trap

After these steps are complete, the vapor that contains the compounds moves with the carrier gas to the detector, where it is analyzed. When the analysis is complete, the results appear on the chromatograph’s interface.

Are certain purge and trap autosamplers better than others?

As with any type of equipment, certain autosamplers receive higher ratings than others. Currently, one autosampler that is preferred by scientists around the world is the Centurion WS Autosampler, which receives excellent ratings in the following categories: analytical superiority, mechanical robustness, productivity, ease of use, and ease of maintenance.

Can purge and trap autosamplers be used in tandem with other autosamplers?

Yes. They are often used in tandem with autosamplers that are designed to analyze compounds that occur at high ppb levels, such as static headspace and dynamic headspace autosamplers.


Laboratory equipment can be a significant investment. But getting the right equipment can make a difference in the quality of a lab’s work. Before you invest in an autosampler, consult with a professional seller of elemental analysis equipment, and ask about the option of buying lab equipment used.

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Source by James T. Rothery