In sorbent tube sampling, what does a blank indicate?

• A. A calibration gas.
• B. A blank is a tube with a loaded sample.
• C. A sorbent tube blank is not exposed to air to assess background contamination from handling or storage.
• D. A blank is a standard reference material.

Answer: (D)

In sorbent tube sampling, a blank is a tube that is handled and stored just like the actual samples but is not exposed to the ambient air being sampled. Its purpose is to reveal any background contamination introduced during handling or storage. If contaminants appear in the blank, they’re coming from the tube, handling, or storage rather than from the air, so you can account for that in the results. This is different from calibration gas, which is used to calibrate instruments, or a tube that actually contains collected sample, or a standard reference material used for calibration or validation.