Which device ionizes a sample using ultraviolet light?

• A. PID (Photo Ionization Detector)
• B. LEL meter
• C. O2 sensor
• D. VOC detector

Answer: (A)

The main idea is that a Photo Ionization Detector uses ultraviolet light to ionize molecules in a sample. A PID emits a UV lamp that sends photons energy enough to knock electrons off many volatile organic compounds. When a VOC absorbs a UV photon, it becomes ionized, producing positive ions and electrons. Collecting those charges generates a current, which the instrument translates into a signal proportional to the concentration of ionizable organic vapors in the air. This makes PIDs particularly sensitive to many solvents, aromatics, and other VOCs. Other devices listed operate by different principles: LEL meters detect flammable gases through catalytic reactions and heat changes, not UV ionization; O2 sensors measure oxygen levels electrochemically, not by ionizing samples; a VOC detector is a broad category, but only a PID uses UV light to ionize the sample.