Photoionization Detection - Thermo Scientific TVA2020 Instruction Manual

Introduction

Photoionization Detection

Photoionization
Detection
1-4 TVA2020 Instruction Manual
A Photoionization Detector (PID) consists of an ultraviolet (UV) lamp of a
specific energy and an ionization chamber (see
passing through the chamber are excited by photons of UV energy and
ionized according to the following equation:
 
R + h
where:
R = most organic/inorganic compounds
These ions are attracted to a collecting electrode, producing a current
proportional to the concentration of the compound.
Whether or not a compound can be detected by a PID depends upon the
energy required to remove an electron from the compound (its ionization
potential). If the lamp energy is greater than the compound's ionization
potential, the PID will detect it. The lamp in the TVA2020 is 10.6 eV.
Because of its smaller dynamic range (0-2000 ppm), the PID is not the
detector of choice for measuring high concentrations of vapors. A PID is
also more susceptible to interference from water vapor than a FID.
However, as a PID does not require hydrogen or oxygen, it is the detector
of choice when fuel is limited or unavailable, or when ambient oxygen
concentrations are low. The PID is also very sensitive to aromatic and
chlorinated compounds, and can even measure some inorganic compounds
that the FID does not detect at all (ammonia, carbon disulfide, carbon
tetrachloride, chloroform, ethylamine, formaldehyde, and hydrogen sulfide,
to name a few).
Figure
R+ + e
–
1–2). Compounds
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