What is a sorbent tube and how does it function in active sampling for volatile organic compounds?

• A. A sorbent tube contains adsorption media to trap VOCs; in active sampling a calibrated pump draws air through the tube so analytes are captured for lab analysis.
• B. A sorbent tube is a passive device that measures humidity.
• C. A sorbent tube generates VOCs for calibration.
• D. A sorbent tube is used to release trapped VOCs back into air.

Answer: (A)

A sorbent tube uses adsorption media packed inside a small tube to capture VOCs from the air. In active sampling, a calibrated pump pulls a known volume of air through the tube, so the volatile compounds are trapped by the sorbent material. After collection, the tube is sealed and taken to the lab, where the trapped analytes are released (desorbed) and analyzed, typically by methods like thermal desorption followed by GC-MS. The pump and flow rate control the volume of air sampled, which is essential for determining the concentration of VOCs in the air.

This is the best description because it directly describes how the sorbent tube traps VOCs and how active sampling uses a pump to draw air through the tube for subsequent lab analysis. The other options describe humidity measurement, VOC generation for calibration, or releasing trapped VOCs back into air, none of which reflect the purpose and function of a sorbent tube in active VOC sampling.