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FID/DELCD Combination Detector - SRI Instruments
FID/DELCD Combination Detector
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The FID detects hydrocarbons & the DELCD identifies which are
chlorinated
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No eluyent needed for the DELCD - operates in gas phase
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Low and high sensitivity modes:
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Detects to the low ppm range, and low ppb range, respectively
The FID/DELCD is one of the most useful detector combinations because it allows the operator to reliably
identify hydrocarbon peaks detected by the
as halogenated or not.
While less sensitive than the
detector, the DELCD is much more selective, eliminating interferences which
would complicate an ECD analysis (such as ambient oxygen). Sample preparation which might be required for ECD work
is not required for the DELCD because of its total selectivity to chlorine and bromine, and because the FID pre-combusts
any contaminants. In the high sensitivity mode (hydrogen off, using dry cylinder air), the DELCD can detect down to the
low picogram range. In this mode, the DELCD is about 100 times more sensitive than when used with the FID in
low sensitivity mode.
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 comverted to CO
2
prior to the DELCD, thereby preventing large hydrocarbon peaks
from contaminating the DELCD. Since the DELCD operates at close to 1000
°
C, it can tolerate the water-saturated
FID effluent and measure the chlorine and bromine content simultaneously with the FID hydrocarbon content
measurement. This is especially useful for measuring chlorinated VOCs under a solvent peak, or measuring PCB
peaks obscured under large amounts of diesel fuel. This detector combination is often used with our
and
which concentrate the sample to achieve lower detection limits
.
The FID/DELCD is supplied with dual amplifiers.
The top FID trace shows the
hydrocarbons in a 100ppm BTEX +
bromoform sample, while the bottom
DELCD trace shows only the
halogenated compounds. The DELCD
completely rejects the large solvent
peak.