Which direct reading instrument ionizes vapors using an internal ultraviolet (UV) lamp?

Which direct reading instrument ionizes vapors using an internal ultraviolet (UV) lamp?

• A. Photoionization Detectors (PIDs)
• B. Colorimetric Tubes
• C. Passive Dosimeters
• D. Filter Cassettes

Answer: (D)

Photoionization detection relies on ionizing airborne molecules with ultraviolet photons from an internal lamp. A photoionization detector uses this UV source to eject electrons from many VOCs; the produced ions create a current between electrodes, and the instrument reads this current as a direct, real-time measure of concentration. Because the response depends on the ionization energy of the compounds, PIDs are especially useful for detecting low levels of volatile organics on the spot and are portable for field use. The other options do not ionize vapors with UV in real time: colorimetric tubes rely on a chemical color change after sampling, not a continuous reading; passive dosimeters accumulate exposure over time and are read later; filter cassettes collect samples for lab analysis rather than providing immediate readings.

Photoionization detection relies on ionizing airborne molecules with ultraviolet photons from an internal lamp. A photoionization detector uses this UV source to eject electrons from many VOCs; the produced ions create a current between electrodes, and the instrument reads this current as a direct, real-time measure of concentration. Because the response depends on the ionization energy of the compounds, PIDs are especially useful for detecting low levels of volatile organics on the spot and are portable for field use. The other options do not ionize vapors with UV in real time: colorimetric tubes rely on a chemical color change after sampling, not a continuous reading; passive dosimeters accumulate exposure over time and are read later; filter cassettes collect samples for lab analysis rather than providing immediate readings.