Flame Ionisation Detectors
The common standard method for measuring organic gas concentration, FID analysers have been used for over 50 years often alongside gas chromatographs. FID analysers work by the pyrolysis of the organic gases in a flame of hydrogen burning at >400˚C in air, producing positively charged ions which induce a current when they hit the negatively charged detector plate. The FID will produce a single measurement of Total Organic Content (TOC) based on the response from the burnt gas.
Often the single value result for organic content is of little use to industrial processes. The FID gives no indication of what species are being measured. For example, a plant operator may only be concerned with chlorinated organic gases passing through the processes, in the presence of other organic species.
Each organic molecule will respond differently to the pyrolysis action in the FID. Some gases such as methane will response very well. Molecules that contain oxidised carbon atoms (C-O bonds) such as alcohols or amines do not respond as well and the FID is not the best technique for speciating out and accurately measuring mixtures of these gases.
Protea can and has provided FID solutions to customers where it is all that is required. However, the availability and analytical power of FTIR analysers has shown many benefits over FID in organic gas measurements. Protea has run a number of studies comparing FID and FTIR in measuring total VOC which shows that for a complete measurement, FTIR is the route to go.
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FID Vs. FTIR >