Detector Systems

Flame ionization detector (FID)

Compounds producing little or no response include:

Rare gases

N

N

Nitrogen Oxides

CO

*CCl

Silicon Halides

CO

 

H O

CS

 

NH

O

 

* Measured at the jet tip.

This selectivity can be advantageous: for example, H O or CS , 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.

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