Which instrument detects volatile organic compounds but may miss inorganic gases and requires calibration?

Which instrument detects volatile organic compounds but may miss inorganic gases and requires calibration?

• A. Infrared detectors identify certain chemical signatures but are limited by line-of-sight and interference
• B. PIDs detect volatile organic compounds but may miss inorganic gases and require calibration
• C. Colorimetric tubes provide pass/fail indications but are not continuous
• D. Multi-gas meters measure several gases at once but may not identify unknowns

Answer: (B)

Volatile organic compounds are detected with a device that uses UV light to ionize most VOC molecules, producing a signal that is roughly proportional to their concentration in the air. This approach is excellent for broadly screening air for organic vapors, but it isn’t reliable for inorganic gases, because many inorganic species either don’t ionize well under the lamp’s energy or yield a weak signal. Readings from this instrument reflect total VOCs rather than identifying specific compounds, so accurate interpretation requires calibration. Calibration uses a known VOC gas, commonly isobutylene, to relate the ionization signal to an actual concentration and to compensate for factors like lamp aging and humidity. This combination—sensitive and fast VOC detection with the need for regular calibration—explains why the instrument fits the description.

Volatile organic compounds are detected with a device that uses UV light to ionize most VOC molecules, producing a signal that is roughly proportional to their concentration in the air. This approach is excellent for broadly screening air for organic vapors, but it isn’t reliable for inorganic gases, because many inorganic species either don’t ionize well under the lamp’s energy or yield a weak signal. Readings from this instrument reflect total VOCs rather than identifying specific compounds, so accurate interpretation requires calibration. Calibration uses a known VOC gas, commonly isobutylene, to relate the ionization signal to an actual concentration and to compensate for factors like lamp aging and humidity. This combination—sensitive and fast VOC detection with the need for regular calibration—explains why the instrument fits the description.