Tubes for Sampling and Analysis

Sorbent tubes can be used to capture many chemical compounds, especially organics, in stack emission, environment or on work places. Sorbent tubes are available as passive solutions or, more common, used in combination with active samplers. In relation to the adsorbing material, a sorbent tube can be used to caputre a specific or groups of compound both for quantitative or quantitive determinations, also in some cases at low ppb levels thanks to the preconcentration effect.

When used in combination with active samplers, the sorbent tube is often composed by different stages, used to capture and evaluate the saturation of the tube itself. In those cases, the flow must pass through the tube with a specific direction.

The material filling the tube can be made of different materials, and it’s defined as “adsorbing phase” or “adsorbent” and interacts with the chemical compound blocking it on its surface through chemical reactions, creating both ionic or covalent intramolecular bondings, or physical interactions, such as with forming van der waals bondings.

IImportant characteristics of the sorbent tubes are the affinity, capability to interact with specific or groups of compounds, and the capability to release efficiently those compounds in particular conditions.
The reverse process is called “desorption” and the procedures which allow it to take place are the chemical or the themal desorption.

With the chemical desorption, an appropriate solvent is used to efficiently extract the sample from the support. For example. volatile organic compounds (VOCs) retained on charcoal tubes, are often desorbed using carbon sulfide.

The chemical desorption process require a skilled laboratory practice since the involved materials can be dangerous and expensive.
In the last years,the thermal desorption practice started to be used also for the sorbent tubes used for environmental or occupational hygiene samplings. This procedure, often automated, allow to extract the sample using high temperatures.