Collector Electrode
Exhaust
Flush
Gas
Capillary
Column
MakeUp
Gas
Lamp
Polarizer Electrode
Quartz ReactionCell
Capillary
Column
Adapter
Capillary
Column
Courtesy of
ThermoFinnigan
Description
eVRating Base qty. cat. #
PID Lamp, Model 103 C
10.2 1.375"
ea.
20676
PID Lamp, Model 108
10.0/10.6 0.781"
ea.
20675
PID Lamp, Model 108-
β
TEX 10.0/10.6 0.781"
ea.
23020
PID Lamp, Model 108
9.6 0.781"
ea.
23021
PID Lamp, Model 107
8.4 0.781"
ea.
23022
PID Lamp, Model 109
11.8 0.781"
ea.
23023
PID Lamp Polishing Kit
kit
20674
Photoionization Lamps
24
PIDOperation
The photoionization detector, PID, is a selective, non-destructive detectormost commonly
used for characterizing aromatic compounds (Figure 19). It has excellent sensitivity (low pg
detection) and provides a linear dynamic range of 3 orders ofmagnitude.
In a PID, a krypton lamp emits photons in the form of light energy at awavelength of
116.6nm and 123.6nm. The photons excite compounds having an ionization potential of less
than 10.2eV. Charged particles produced in thismanner pass through a reaction cell with an
electrical potential of 50 to 200 volts, producing an electrical charge that ismeasured as a
signal. Sensitivity is a function of the chemical structure of the analyte, including the num-
ber of carbon atoms, the nature and position of functional groups, and the position of double
or conjugated double bonds.
10
For suitable analytes, a PID is 10-timesmore sensitive than an
FID. Compounds such as benzene (9.3eV ionization potential) have ionization efficiencies of
less than 0.1%, allowing themajority of the sample to pass through the detector unaffected.
Evenwith thisminute portion of the sample ionized, sensitivity for aromatic compounds is
measured at the pg level.
PIDMaintenance andTroubleshooting:
It is very common for silicone from column bleed
to collect on the PIDwindow and reduce transmission from the lamp. Reduced sensitivity
for all components is evidence of this condition.We recommend cleaning thewindow on a
regular basis, using amild abrasivematerial such as iron oxide.Alumina powder ismore
abrasive than iron oxide and can scratch the lens. Thiswill reduce sensitivity. Create a slurry
with the powder, scrub thewindow, then rinsewith acetone ormethanol.Avoid touching the
cleanwindow. If sensitivity is not restored, replace the lamp. Dead volumewithin a PIDwill
produce broad peaks, andmight cause peaks to tail. PIDs designed for packed column sys-
tems have a cell volume intended for high flow rates.When using these detectorswith capil-
lary columns, 20-30mL/min. ofmake-up gas is required tominimize dead volume and, in
turn, reduce peak tailing. Newer PID designs have smaller cell volumes that are compatible
with capillary columns.
Figure 19.
Diagram of a typical PID.
10. JessieCrockett Butler, “TandemDetector Technology forGas Chromatography.”Environmental
Analysis Technical Report No. 9110, p3. ThermoFinnigan, GC andGC/MSDivision, Austin, TX.
