About FID

[wufi2004]

How can I get the VOC concentration from FID- and calibration curve? Is there some procedure?

What's the relationship between Chromatogram and FID response?

 

[mohtogh]

Chromatograph can give you concentration of each hydrocarbon separately, while FID just report total concentration of carbon in sample, and then you ( or your instrument)can converts it to equivalent methane, or every hydrocarbon that you want.For a FID analyzer, we can have calibration curve based on methane, ethane or each hydrocarbon that you want, but not all of them at a time. So, we can not extract concentration of each hydrocarbon, from FID response.
Hope this help.

 

[jppmj]

I use FID for measuring VOC concentration in the following way.
1 With fresh air or through an activated carbon filter I adjust the ZERO.
2 I adjust the span with a known reference gas (usualy propane in air at 75 ppm propane)
3 I read ppm in the gas to be measured for example 55 ppm equivalent propane.
4 If we don't know the type of VOC we have to measure we simply say VOC 55ppm equiv propane or 55 x 44/22.4 = 108mg/Nm3 equiv propane or best 55 x 36/22.4 = 88.4 mg C/Nm3.
5 If we know the type of VOC, for exemple Methylen Chloride, there is a multiplication factor to be used for conversion of ppm propane to mg Solvant/NM3.
I hope this will help you (sorry for my bad english)
JPPMJ

 

[chemecheng]

Hi, chromatogram shows FID (detector) response over time. Each response corresponds to a certain amount of VOC, and that correspondence is defined when you calibrate. So, first calibrate using standards containing target VOCs. Calibration curve could be three to six points, depending on the accuracy needed. Also pick convenient calibration range depending on your type of work, yet don’t forget about FID and column limitations. FID has a good linearity but you may need to do some dilutions if you are using pure or high products.
Look at it this way, lets say we want to read voc1, range 100ppm-2000ppm. I'd get voc1 standard and do, for example, (100,200,800,1200,1600,2000)ppm after each one FID would give response (best taken as area of the pick), for example, (xvfx,xxgfxx,xxxhghxxx,xxghgdxx,xxxxdrxx)then yourself or software plot response=function (amount). Now you are ready to measure.