glycol analyze using FID

Discussions about GC and other "gas phase" separation techniques.

7 posts Page 1 of 1
Hello
i use Agilent 7890B GC-FID to analyze glycol in water. column is SPB-1000, 30X0.25mmx0.25um. injection value is 1ul, spitless(directly inject sample without extraction).
The temperature program is 50, 20c/min till 250.
the compounds are EG(BP=197),PG(BP=188),DEG(BP=245),TEG(BP=285).
My question is with this temperature program, TEG can not elute. But some lab staffs said TEG will elute. when i searched online, the final temp of some method is 200, and TEG will elute at 25 minutes. i am so confused.
Can someone explain this to me
thank you
How long do you hold the inlet in splitless mode?

What is the inlet temperature?

Is it possible it is not getting onto the column or the peak is so broad that it doesn't look like a peak at all.

1ul is a lot of water to inject in splitless mode. Most inject 1ul of water in split mode. You could be having a backflash of the water when it evaporates and that could be causing problems getting the TEG on column.

Try using a split injection at 10:1 split ratio and see if that improves things.
The past is there to guide us into the future, not to dwell in.
Hello James_ball
thank you for your information. The inlet temperature is 250. inlet hold time 1min. The peak is tailing. For low concentration, the tailing is very bad, high concentration is ok but still tailing.
My major concern is if TEG could elute because final temperature is 250
i have a chrom with ,but i do not know how to attach it.
thanks again
https://ibb.co/NLTJgrW
this is the chromatography i loaded
thanks again
We always used trimethylsilyl derivatization for glycols, from EG through TEG. We dissolved in DMF or pyridine, then derivatized. Non-polar capillary.

Are your analytes at trace levels???
Hi,
thank you for your information
Yes, my lab does trace glycol. But i did not use extraction solvent to extract glycol, directly inject water sample into GC-fid(maybe filter water sample).The method just set up, but it is not good. My question is final temperature of oven is 250, TEG BP is 284. How does TEG can elute?
thanks again
If the vapor pressure at 250c is high enough it will elute from the column. The separation is not only by boiling point but also by interaction between the stationary phase and the carrier gas. If the analyte wants to be in the carrier gas more than in the stationary phase at 250c or less then it will pass through the column.

Tailing can come from many things, not only boiling point above column temperature.

Here is TEG on a wax phase column, eluting at or below 250C
https://www.restek.com/en/pages/chromat ... GC_CH00337

Here it elutes about 240C on a 1 phase column
https://www.restek.com/en/pages/chromat ... GC_CH00335

On both they use inlet temperature of 275C and split injection mode, this could help with the tailing of the TEG. If you worry about the higher inlet temperature degrading the inlet end of the column, try adding a guard column which has no stationary phase to act as a temperature buffer between the inlet and column. 0.5 to 1m of guard column will protect the analytical column from high inlet temperatures so you can increase it enough to make sure the TEG gets vaporized quickly and onto the column, but you probably won't need it.
The past is there to guide us into the future, not to dwell in.
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