PHOTO IONIZATION DETECTOR ( PID )

The PID detector consists of a special UV lamp mounted on a thermostatted low volume flow-through cell. The temperature is adjustable from ambient to 250ºC. The 10.6 electron volt UV lamp emits energy at a wavelength of 120 nanometers, which is sufficient to ionize most aromatics ( benzene, toluene, xylene, etc. ) and many other molecules ( H2S, hexane, ethanol ) whose ionization potential is below 10.6 ev. Methanol and water, for instance, have ionization potentials greater than 10.6ev and do not respond on the PID.

Detection limits for aromatics are in the low picogram range ( ppb ) and because the PID is non-destructive, it is often run in series with another detector ( FID/DELCD ) for multiple chromatograms from a single injection. Use of the PID is mandated in several EPA methods ( 8021, TO-14 etc. ) because of its sensitivity and selectivity. The PID is also able to run on air carrier (see the new Gas-less GC^TM), which can be useful in situations where no gas ( helium, hydrogen, nitrogen ) is available, or stream monitoring applications where no column is used to separate compounds but rather the entire stream of sample is directed through the detector.

Unlike other PID designs, the lamp on the SRI PID can be removed easily without tools for periodic cleaning of the lamp window, and lamps last far longer on the SRI PID because only the lamp window is heated, not the body of the lamp.

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