Detector Systems
Flame ionization detector (FID)
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Compounds producing little or no response include:
Rare gases N N
Nitrogen Oxides CO *CCl
Silicon Halides CO
H OCS
NH O
* Measured at the jet tip.
This selectivity can be advantageous: for example, H OorCS , used as
solvent, do not produce large solvent peaks.
The system is linear for most organic compounds, from the minimum
detectable limit through concentrations greater than 10
times the
minimum detectable limit. Linear range depends on each specific
compound; it is directly proportional to sensitivity of the FID toward the
given compound.
In general, where sample components of interest are in high
concentration, increased air flow may be necessary (up to 650 ml/min).
Where components of interest are in low concentration, reduced air flow
rates are acceptable (375 to 425 ml/min).
For maximum sensitivity, it is recommended that a standard sample be
made containing components of interest in concentrations expected. By
experimenting with different carrier, air, and H
flow rates, the standard
is used to determine flow rates giving maximum response.
