Photo Ionisation Detectors feature an ultraviolet lamp that emits photons. The compound inside an ionisation chamber then absorbs the photons. Photoionisation occurs when an atom/molecule absorbs light from energy, which insufficient levels causes an electron to leave, creating a positive ion. Ions produced during this process are collected on electrodes, and the current generated provides a measure of the analysed substance.
 
The PID detector can measure the electrical current, and converts this to the concentration of VOCs present. It detects only certain VOCs and will not pick up gases in the air like carbon dioxide. Because only a small fraction of the analyte molecules are actually ionised, this detection method is non-destructive. It can be used in conjunction with another detector to confirm analytical results.

Advantages

Gas detectors like Photo Ionisation Detectors provide many advantages; the most important advantage is the safety of workers. A PID detector is ideal for oil and gasoline spills, leaking cylinders or gas valves, hazardous materials incidents, and other emergency leak situations.

VOCs are toxic and often combustible materials that can endanger workers, even in low concentrations. For additional safety, a Photo Ionisation Detector should be installed in every industrial facility that could be exposed to VOCs.