We hosted an educational webinar recently with Werner Haag Ph.D, a senior chemist with Ion Science USA and author of “The PID Handbook- Theory and Applications of Direct-Reading Photoionization Detectors.” I think it provided a great explanation of how PIDs work, what and where they can measure and, importantly, what they can not measure.
Here is basically how they work: PIDs use ultraviolet light to excite gas molecules, which results in the temporary loss of an electron. These molecules become ionized and create an electrical charge. This electrical charge of these positively charged ions becomes the signal for the detector. So, the greater the concentration of gas, the greater the charge, and the greater the reading to the detector.
When I think of measuring for volatile organic compounds (VOCs) I typically think of industrial or hazmat applications, where exposure to gases cause an immediate concern. However, PIDs can be used in indoor air quality surveys where long term exposure to VOCs can be an issue. There are a number of VOCs that can be found in many structures including building materials, cleaners, solvents, paints and gasoline.
The webinar also provides a number of real world examples and walks through the process of measuring benzene. It’s a good mix of theory and practical application.
If you have the time I highly recommend watching the whole webinar:
If you are looking for PIDs for industrial applications: http://www.raeco.com/brands/ion-science.html
If you are looking for PIDs for indoor air quality issues: http://www.raeco.com/products/iaq/tsi-q-trak-7575.html