ION Science PID Response Factors
PID Response
Photoionization Detectors (PIDs) respond to a broad range of organic and a few inorganic gaseous and volatile chemicals (‘volatiles’). In order for PID to respond to a volatile, the photon energy of the lamp must be greater than its ionization energy (IE). ION Science PIDs are available with lamps emitting light of maximum energy of 10.0 eV, 10.6 eV, and 11.7 eV. This Technical Article lists the response factors (‘RF’s’) for over 900 volatiles with PID incorporating these lamps. The RF relates the sensitivity of PID to a volatile to the sensitivity to the standard calibration gas isobutylene. The higher the RF, the lower the sensitivity.
Isobutylene as Reference Gas
Ideally, the PID response to a chemical volatile would be calibrated by using a low concentration of the chemical in air. However, this is often not practical. Isobutylene is then used to calibrate PID, and a Response Factor (RF) used to convert the isobutylene calibrated measurement to a measurement of the target volatile”
Concentration of target chemical = isobutylene calibrated measurement x RF
For example, the RF of anisole is 0.59 with a 10.6 eV lamp. That means 0.59 ppm anisole delivers the same PID response as 1 ppm isobutylene. A 10 ppm response to anisole, from a isobutylene-calibrated unit would indicate:
Concentration of anisole = 10 ppm x 0.59 = 5.9 ppm
In ION Science detectors, RFs are pre-programmed into a compound library and can be called up to make the PID read out in units of the chemical of interest. For example, to indicate a measurement of acetone with a detector engaging a 10.6 eV lamp, an instrument is calibrated with isobutylene, and acetone is selected as the target compound, for which the RF is 1.17. The detector then displays directly the concentration of acetone by multiplying the isobutylene equivalent response by the response factor.
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