48
GCDetectors
FID/DELCDCombinationDetector
• TheFIDdetectsHydrocarbons and theDELCD
identifieswhichareHalogenated
• NoElectrolytesneeded for theDELCD
• HighandLow sensitivitymodes
• Detects to theLowppm range
The FID/DELCD is one of the most useful detector
combinations because it allows the operator to reliably
identify hydrocarbon peaks detected by the FID as
halogenatedor not
ThetopFIDtraceshows thehydrocarbons ina100ppm
BTEX plus sample, while the bottomDELCD trace
shows only the halogenated compunds. TheDELCD
completely rejects the large solvent peak.
FID
DELCD
While less sensitive than the ECD detector, the
DELCD is much more selective, eliminating
interferences which would complicate an ECD
analysis. Sample preparation which might be
required for ECD work is not required for the
DELCD because of its total selectivity to chlorine
andbromine, andbecause the FIDpre-combusts
any contaminants. In the high sensitivity mode
(hydrogen off, using dry tank air), the DELCD
can detect down to the low picogram range. In
this mode, the DELCD is about 100 times more
sensitive thanwhen usedwith the FID exhaust in
the low sensitivitymode.
The DELCD measures the ClO
2
present in the FID exhaust gas. Because the FID combusts the sample
upstream of the DELCD, all hydrocarbons are converted to CO
2
and H
2
O prior to the DELCD, thereby
completely preventing large hydrocarbon peaks from contaminating the DELCD. Because the DELCD
operates at close to 1000°C, it can tolerate the water saturated FID efluent andmeasure the chlorine or
brominecontentsimultaneouslywith theFIDhydrocarboncontentmeasurement.This isespeciallybeneicial
for measuring chlorinated VOCs under a solvent peak, or inmeasuring PCB peaks obscured under large
amountsof diesel fuel. Thisdetector combination isoftenusedwithour Thermal Desorber or Purge&Trap,
which concentrate the sample to achieve lower detection limits.
8690-2026
FID/DELCDdetector
