Chromatography Forum

Hi,

This is my first topic on this forum, and I thank you for your help.

We are trying to analyse a mix of Methanol and Ethylene glycol in water on a GC-FID. We think the concentration of both are definitely over 10%. Since the equipment is one of a "not-so-rich" university that cannot really afford to waste a column.

I was thinking of diluting the sample at a 2% concentration in ether.I was just wondering, after reading at a few places that water can cause damage to a GC column, if having a concentration of 1,8% of water injected could be problematic?

Hi
The problem of water as solvent is the volume expansion in liner, it's high and there can be backflash in the inlet. There are other topics that talk about it.
Can you try to analyse the sample with headspace?

At the concentration you describe, water shoulld be no problem - even for a carbowax type column. (My column of choice for the analytes you are measuring).

Just be sure that you do not have a lot of non-volitile materials or corrosive materials in the water.

In a 1 microliter injection you will be injecting less that 0.02 microliters of water. If you calculate the expansion volume of 0.02 microliters water and of 0.98 microlters ether, you will see that the effect of water on expansion volume can be neglected.

I would dilute my sample in water and use GC conditions/column like in <USP611>, using a 0.2 to 0.5ul injection.

We use those conditions for our alcohol analyses routinely. We've also used those conditions for ethylene glycol and diethylene glycol, the same column that USP details in its glycerin and propylene glycol monographs.

I used to test aqueous samples for ethanol and propylene glycol in the range of 10-30% each analyte routinely by diluting 1:50 in acetone and running on a polyethylene glycol capillary column 0.53mm diameter. Worked like a charm.