PID calibration isobutylene is used for which detector?

• A. Methane
• B. Isobutylene
• C. Ethylene
• D. Propane

Answer: (D)

In PID calibration, you pick a reference gas whose response in the detector is well understood and stable. Isobutylene is used because its ionization energy and molecular structure produce a reliable, repeatable signal in a photoionization detector, making it a good standard for calibrating how the instrument will respond to hydrocarbon vapors. When the goal is to optimize a detector that’s meant to sense propane, using isobutylene as the calibration gas gives a calibration reference that closely represents the behavior of propane in the same detector, helping to set the correct sensitivity and ensure accurate readings in practice. Methane would be harder to ionize with common PID lamps, and ethylene or other gases may not align as well with propane’s response, so isobutylene is the preferred calibration reference for propane detection.