Please note that FID will not respond to gases like CO, CO2 etc, whereas, TCD will detect them. But the problem is TCD sensitivity is much lower than FID. If CO and CO2 are present in very low concentration, then TCD will not be able to give a proper signal. In that case, FID can be used, but CO and CO2 should be converted to Methane using a Methanizer. In the methanizer, CO and CO2 will be catalytically reduced to CH4 and FID will detect CO and CO2 as Methane. Methane being a hydrocarbon, produces good sensitivity in FID.

HI, Tharani Kulandaivalu it's all about the sensitivity of FiD is fairly high for hydrocarbons because the respond of FiD is proportional to the organic carbon content in the compound. the sensitivity value is amplified with the increasing of effective carbon number in the compound, for example, c3h8 has an effective carbon number of 3.0, ethane 2.0, etc8,9.

https://analyteguru.com/detector-detective-part-i-flame-ionization-versus-thermal-conductivity/

Tharani Kulandaivalu You can chec this site

Due to the type of analyte, an appropriate detector should be used with specific sensitivity degree. Also, the molecular structure of the bonds analyte in terms of placement in some of functional groups is influential.

the sensitivity of GcYFiD is fairly high for c3h8 because the respond of FiD is proportional to the organic carbon content in the compound. the sensitivity value is amplified with the increasing of effective carbon number in the compound, for example c3h8 has an effective carbon number of 3.0, ethane 2.0, etc8,9.

The sensitivity of the GC-FID are 66 times higher than GC-TCD method.

Thermal conductivity (TCD) is a commonly used detector in gas chromatography. ... While flame ionization detector (FID) can provide very good resolution.

Hi Tharani,

Other folks have mentioned good points about the fact that generally FIDs are generally more sensitive to carbon-containing analytes than are TCDs. Some understanding of the different detectors can help explain why this is the case:

- FID typically works by first methanizing your sample over a nickel catalyst, then burning it in a hydrogen flame. The ions generated during this combustion process will be detected. In this way the instrument is able to "count carbons" by distinguishing the signal generated by burning organics relative to burning hydrogen.

- TCD works by measuring a deviation in thermal conductivity between your sample and your carrier gas. Since thermal conductivity is related to molecular weight, you can actually change a TCD's "sensitivity" to a given analyte by altering the carrier gas. For instance, if you're trying to detect CO with an N2 carrier gas (basically same thermal conductivity), you will be out of luck; however, if you use hydrogen or helium as a carrier gas instead of nitrogen, then you may actually end up seeing a reasonable peak for CO.

Hope that is helpful! Let me know if you have any questions about what I've mentioned.

Best wishes,

Kindle

Thank you all for your clarifications. Dr Debanjan Chatterjee the CO concentrations in my product is very low, about 0.01mol%. The tiny CO peak in TCD chromatogram making me difficult to integrate, even if i set the slope sensitivity to 1. At the same time, FID forms a fairly visible peak for CO at the same retention time. Can i just take integration value of CO peak formed by FID to calculate the mol% of CO in my sample?

Tharani Kulandaivalu I'd highly recommend using FID for CO quantification rather than TCD. That is how our group approaches CO measurements. It would be best to use a calibration curve to interpret your FID integration.

Dear Dr Kindle Williams Thank you very much for your suggestion. Will definitely take your advice to quantify CO in my sample.

Carbon monoxide and carbon dioxide are not detectable by FID !!!

There is an error in you method/samples. How you separate (define the column) the CO from the gas matix? Maybe you have CH4 there?

It is possible to detect CO by FID only if you have a methanizer before the FID.

regards,

GB