Chromatography Forum

hi .
iam using the GC . Agilent GC 7890B for oil analysis especially for Fatty acid methyl ester . and i always set the oven température to 180°C .
my question is why 180°C and not 200°C or more ? i mean what would happen if it's changed how could that effect the results ?
thank you.

In general the higher the temperature the faster compounds travel through the column. Is this iso- thermal or is 180 the starting temp?

In general the higher the temperature the faster compounds travel through the column. Is this iso- thermal or is 180 the starting temp?

180°C is the starting temp.
well, i have no problem with this temp but i just want to know how does it effect the sampls

You definitely need to read a book* on gas chromatography or attend a training.

* - or viewtopic.php?f=2&t=26882#p127645

I assayed fatty acids from soaps and consumer products as methyl esters for 4 decades. We've used packed columns, isothermal and programmed, wide-bore capillaries, narrow-bore capillaries, etc, split and non-split.

In other words: lots of ways to get there. I like cyanopropylsilicone columns best, better than DEGS or PEG columns.

Important when using split injection is to make sure that the inlet temperature minimizes split discrimination issues over your fatty acid range.

I recommend buying a standard reference mixture of fatty acid methyl esters and using that to calibrate, you may want to incorporate response factors.

hi .
iam using the GC . Agilent GC 7890B for oil analysis especially for Fatty acid methyl ester . and i always set the oven température to 180°C .
my question is why 180°C and not 200°C or more ? i mean what would happen if it's changed how could that effect the results ?
thank you.

Lower starting temperatures will cause compounds to retain longer on the column if using the same temperature ramp, but will allow greater separation in the early eluting compounds. Higher starting temperature will have the opposite effect. Many compounds elute from the column due to both interaction with the column phase and their boiling point, so temperature will change their elution time.

Also you have to consider the injection solvent, if your column temperature is below the boiling point of the solvent, the solvent will condense on the beginning of the column. This can be used to focus analytes but it can also cause peak distortions, so it is a trade off as to what you want to accomplish.