Misconceptions in Using Photoionization Detectors

Photoionization detectors, or PIDs are a great way to find volatile organic compounds (VOCs). What is photo ionization? Basically, it involves using ultraviolet light to break molecules into positively charged ions. When molecules absorb high energy UV light they become excited, resulting in temporary loss of electrons and the formation of positively charged ions. This electrically charges the gas and these ions produce an electric current, which is then the signal output for the detector. The greater the concentration of the gas, the more ions are produced, the greater the current, and the greater the reading.

However, there are a number of misconceptions of what a PID can and cannot do. Robert Henderson, VP of Business Development for BW Technologies, wrote a nice article about it for Environmental Technology. Here’s a quick rundown of the misconceptions:

  1. Changing the PIC correction factor (CF) or choosing a chemical from the on-board library makes the instrument readings specific for that substance
  2. I can’t use a PID because I need substance-specific readings
  3. I can’t use a PID because I never know which VOC is producing the reading
  4. You can use any manufacturers correction factors for your PID instrument
  5. If a 10.6 eV lamp is good, and 11.7 eV lamp must be better
  6. PIDs can be used to replace traditional LEL sensors
  7. PIDs can’t be used in the presence of methane
  8. PIDS don’t work in high humidity
  9. PIDs must include a built-in pump or fan to obtain readings
  10. PIDs can be used to replace many common substance-specific electrochemical sensors

If any of these sound like something you have heard before, I encourage you to read the full article: Questions, myths, and misconceptions about using photoionization detectors (670KB PDF).

Looking for personal and portable photoionization detectors? RAECO offers several, so there’s sure to be one to match your specific application.

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