What uses Ultraviolet light to ionize the particles to determine VOCs?

• A. Mass spectrometer
• B. Infrared sensor
• C. Electrochemical sensor
• D. Photo Ionization Detector (PID)

Answer: (D)

Photo Ionization Detector uses ultraviolet light to ionize VOCs. In this approach, a UV lamp emits photons energetic enough to knock electrons off many volatile organic molecules present in the sampled air. The resulting ions and electrons create a small current between electrodes, and the detector measures this ion current. The signal is proportional to the concentration of VOCs, making PID a sensitive method for detecting a wide range of VOCs at low levels.

This stands apart from infrared sensors, which detect VOCs by how much infrared light they absorb rather than by ionizing them. Electrochemical sensors rely on redox reactions at electrodes to produce a current, not on UV ionization. Mass spectrometers do ionize molecules too, but they use different ionization methods and analyze the ions’ mass-to-charge ratios rather than producing a straightforward current from UV ionization. So the description aligns with a Photo Ionization Detector.