|Use:||Flame-ionization detectors (FIDs) are most useful for identifying TPH and PAH.|
Portable FID instruments detect compounds by using a sampling pump to feed air into a mixing chamber. The mixture is ignited as it passes over a pure hydrogen flame which breaks down the organic molecules and produces ions (atoms or molecules that have gained or lost electrons and thus have a net positive or negative charge). The ions gather on a collection plate where a current is generated as a result of the high voltage applied across the detector and the organic ions and electrons present in the gas. The magnitude of the current is proportional to the concentration of organic vapors within the gas. FIDs are also commonly used as detectors in portable gas chromatographs and have several advantages over photo ionization detectors (PIDs) including a wider measuring range and response to all hydrocarbons including methane. In addition, FIDs do not give false positive readings to water vapor.
1. Non-Halogenated VOCs
2. Non-Halogenated SVOCs
3. Some low molecular weight halogenated VOCs
Primarily non-halogenated VOCs and halogenated VOCs. FIDs are sensitive to a larger number of VOCs than a PID (including low molecular weight compounds, such as methane, ethane, and certain toxic gases with high ionization potential, such as carbon tetrachloride and hydrogen cyanide).
|Requires extraction to liquid or gas phase||Requires extraction to liquid or gas phase||BETTER|
|Selectivity:||Technique measures the contaminant indirectly. FIDs will provide the user with a total concentration of VOCs present. Instruments are not compound-specific and readings may vary from the actual air concentrations depending on the ion potential of the compound. Generally, accurate hydrocarbon readings can only be determined for the calibration gas. Other hydrocarbon concentrations can be roughly determined using manufacture-supplied conversion charts.|
|Susceptibility to Interference:||High.|
|Detection Limits :||100-1000 ppb (soil); 1-50 ppb (water).|
|Turnaround Time per Sample:||Minutes.|
ASTM Standards/EPA Methods:
No applicable ASTM standards or EPA methods are cited for this technology.
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