In VOC sampling with sorbent tubes, which statement best defines breakthrough?

• A. Breakthrough is the limit before analysis.
• B. Breakthrough occurs when sorbent capacity is exceeded and analytes pass through the tube.
• C. Breakthrough is when the sorbent breaks.
• D. Breakthrough is the loss of target compounds due to sorbent capacity being exceeded.

Answer: (D)

Breakthrough in sorbent-tube VOC sampling means the sorbent has reached its capacity and the analyte can no longer be retained, so it passes through and is lost from the collected sample. This loss occurs specifically because the sorbent’s capacity is exceeded, which is why this definition best captures the concept. It's not just a generic limit or a physical break of the sorbent; the key point is that exceeding capacity leads to analytes slipping through and not being captured, compromising the sample. To prevent breakthrough, use appropriate sampling volumes, shorter collection times, or a sorbent with greater capacity or multiple sorbents in series.