FID vs. TCD

Chromatography Forum: GC Archives: FID vs. TCD
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Friday, April 11, 2003 - 09:29 am:

I want to rewrite a method using a GC w/FID; however, the original method used a GC w/TCD. Is it possible?


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Benjamin on Friday, April 11, 2003 - 10:30 am:

Dear Anonymous;

It is possible, but it would be difficult. The detectors work on different principles, and the responses and linear ranges are likely to be extremely different as well.

If you want to try it, the best way I can think of is to analyze a known sample by FID and compare the results with those obtained by TCD. Quite likely the sample needed will be much less, and a new calibration solution and procedure will be required.

Good Luck;

Benjamin


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Friday, April 11, 2003 - 12:43 pm:

Thanks, Ben! I'll try that.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Monday, April 14, 2003 - 04:05 pm:

It also depends on the nature of your sample. FID cannot be used to detect CO2, N2, or O2, for example.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Tuesday, April 15, 2003 - 07:44 am:

If your compound is organic and therefore responds to FID, this should be straightforward and also easier and more sensitive than using TCD. Use same column, and show results to be comparable.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Leon on Thursday, April 17, 2003 - 10:11 am:

There is another thing to watch when replacing FID by TCD. In lab GC instruments equipped with optional FID and TCD, the latter might be designed to primarily work with packed columns. As a result, the TCD might not be as fast as the FID and as it might be necessary for a capillary column. This might cause a minor, or severe, or even total loss of resolution of some peak pairs.

Example. In Agilent 5890, 6890 and 6850 GC, the FID data rate is (as far as I remember) 20 Hz in the first place and up to 200 Hz in the last two. The TCD data rate is 5 Hz in all these instruments. As a result, for peaks that are 1 or 2 sec wide (at half height), a noticeable loss of resolution can take place when FID is replaced with TCD. For the peaks that are substantially narrower than 1 sec, a severe or even total loss of resolution can occur.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Monday, April 21, 2003 - 07:20 pm:

I think you may need two identical columns to get a better results with TCD to flow balance


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