Chromatography Forum

I know that the purpose in the inlet is to have a sufficiently high enough temperature to flash the mixture components. I've also read that one should use as low a temperature as that achieves that goal. I also know that the inlet temperature should not be so high as to decompose the mixture. My question is what effect or advantage if any should I expect by raising my inlet temperature 20-30 degrees as long as no new peaks appear from decomposition?

Thanks for all replies.

The best answer you can get exactly tailored to your specific compounds and method parameters would be if you compare chromatograms with current inlet temperature against chromatogram with increased inlet temperature by 20-30 deg.

The best answer you can get exactly tailored to your specific compounds and method parameters would be if you compare chromatograms with current inlet temperature against chromatogram with increased inlet temperature by 20-30 deg.

Thus far I do not see a significant difference between my 220C and 250C inlet temps. I looked at area counts, peak height, and peak width. Unless someone can provide further guidance I will default to the lowest temperature that flashes the components in my mixture.

I was hoping to learn that the inlet temperature had some effect on the chromatography, as I attempt to optimize my method for peak shape, retention time, and response.

What compounds are you analyzing for? What detector are you using? What solvent are you injecting and how much?

If you don't see any inlet discrimination then leave temp. as it is.

Rule zero apllies; if it ain't broke, don't fix it. If the method works at a given inlet temperature, you have no reason to change it.

Higher temperatures can improve response of higher boiling components, but if they are already well evaporated then you won't see improvements.

The biggest effect would be if your oven is colder than the solvent boiling point and you get the solvent effect versus having it warm enough to keep the solvent evaporated as it passes through the column.

Hi!

I have also been some trials this week with inlet temperature. In my case, I tested 210, 250 and 290 ºC. I am trying to quantify amphetamine and it is a thermolabile compound, so we started with 210 ºC...without taking into account that its boiling point is 203 ºC .
210 is so close to the bp that the peaks of the first levels of calibration were pretty small (S/N<10) and the repetibility of the areas was very bad.
Then we tried 250 and the areas were much better.
At 290, the repetibility of the areas at some points of the curve, mainly the most concentrated, was very bad, both for the analyte and for the IS... so I guess that perhaps something happened at that temperature. Finally, I think we will chose 250ºC since it seems to give the most optimal results.

I hope that helps... I'm not an expert at GC, learning every day and coming to conclusions from my results but with any expert to confirm them I guess at the end it is about trying and see what give you the best results.

Hi!

I have also been some trials this week with inlet temperature. In my case, I tested 210, 250 and 290 ºC. I am trying to quantify amphetamine and it is a thermolabile compound, so we started with 210 ºC...without taking into account that its boiling point is 203 ºC .
210 is so close to the bp that the peaks of the first levels of calibration were pretty small (S/N<10) and the repetibility of the areas was very bad.
Then we tried 250 and the areas were much better.
At 290, the repetibility of the areas at some points of the curve, mainly the most concentrated, was very bad, both for the analyte and for the IS... so I guess that perhaps something happened at that temperature. Finally, I think we will chose 250ºC since it seems to give the most optimal results.

I hope that helps... I'm not an expert at GC, learning every day and coming to conclusions from my results but with any expert to confirm them I guess at the end it is about trying and see what give you the best results.

That is how most of us learned what works and what doesn't, simple trial and error. That is probably why I like method development more than routine production If you really want a challenge try environmental samples, so many different analytes and so many different matrix and all need to be run at the same time.

One issue with raising the inlet temperature can be that, depending on your solvent, injection volume, etc., you will begin to see excessive backflash of your solvent, leading to poor repeatability. Restek has a solvent expansion calculator tool that you can use to check your expected backflash level for various inlet temperatures.