Breakthrough in VOC sampling is often observed when sorbent capacity is exceeded. Which statement best describes its effect?

• A. It decreases sample volume.
• B. It increases adsorption.
• C. It results in loss of target compounds.
• D. It improves selectivity.

Answer: (C)

Breakthrough happens when the sorbent capacity is reached and can no longer hold additional VOC molecules. Once all the adsorption sites are occupied, any remaining analyte in the air stream isn’t captured and simply passes through the sorbent bed. That means some target compounds are not collected for analysis, leading to a loss of those compounds in the final sample. In practice, this causes underestimation of the true air concentrations because part of the VOC load has bypassed the capture system.

Think of it like a sponge that’s already saturated with water; when you try to squeeze more water through, it can’t hold it all, so some water drips through instead of being absorbed. The key takeaway is that breakthrough reduces capture efficiency and results in missing (lost) target compounds, not changes to sample volume, adsorption capacity in a positive sense, or improved selectivity.