Chromatography Forum

Hi all,

I was wondering how I can tell definitively if a PEG (Restek stabiliwax) column is non functioning. I had it installed on a GC with a ssl inlet and could not get FAME peaks to separate. All i would see is a long tailing solvent peak, however the peak tails only until the 10 minute mark, where, the bulk of the FAMEs would normally have run off the column.

So, I installed it onto a GC with on column injection and see exactly the same thing. I have also injected a mix of methanol and IPA in h20 onto the column via headspace injection and can get two separate peaks, but they are badly tailing.

Am going to order a new one but want to be absolutely sure before i spend $500...Thanks.

PEG columns are susceptible to damage by water and oxygen as well as reactive components (PEG contains free OH-groups). Tailing with polar components points either towards dirt on the column or a damaged phase.

As you don't seem to have to lose much with that column, there are basically two ways to go after trimming ca. four windings of the column:

1.) Mount it to the GC, purge it with oxygen-free and water-free carrier gas at room temperature for around 20 min., followed by a ramp of around 10°C/min to 20°C below the maximum isothermal temperature. Condition the column and check the standing current of your detector. If the bleeding subsides, you have either toasted the phase completely or removed the contaminants.

2.) Rinse the column with an appropriate solvent which is compatible with the column phase as well as able to purge the suspected contaminants out. Then follow procedure 1. A solvent rinse should always be the last resort but if you have indeed (reactive?) contaminants on your column it might be the way to go.

Please let us know how things develop.

To avoid having to deal with PEG columns for FAMEs, we use cyanopropylsilicone phases like SP-2330.

CPG,

I'll have to check the method, but I believe it says if you use cyano phase columns, you will get co elution of the C:19 internal standard and one of the C:18 fame peaks. It is the latest version of EN 14103

Not quite sure about that though.

You have to be very careful using PEG column, any leaks can damage the column. as it was previously said, oxygen and moisture degrade the PEG faster than in other phases. It is good for FAMEs, and if you want to stick with PEG, you can chose PEGs specifically designed for FAMES, such as OMEGAWAX (supelco) or FAMEWAX (restek)

Also, if you have ran an aqueous solution into the column, yeah, you have probably degraded the column already.

what types of FAMEs are you looking for?. People tend to use the cyano phases for FAMES (SP-2330, SP-2560), but those are for more challenging separations of cis/trans FAMES. Even using 100-m columns is quite common for those analysis.

column was definitely dead. Get nice sharp peaks with new column. Can now separate methanol and isopropyl alcohol and getting good calibration curve for EN 14110.

However EN 14103 FAME analysis (%Ester content) i am getting a huge solvent peak, I don't think I am splitting enough sample out of the inlet. I have 100ml/min off the split vent, 3ml/min off the septum purge, and 2-3mL/min off the column @50 kPa. The method states : 100ml/min off split vent, 70kPA carrier, and 1-2 mL/min off column. Purge valve is on the whole time

Should I turn up the septum purge flow?

Thanks,

I would not think so.

Your method states a split of 100 to 50:1. You are splitting 50 to 33:1, about twice as much sample is entering your column.

If your column flow is correct for your column and not too high then increase your splitter flow to about 150 mL/min.

Or you can reduce your injection volume.

best wishes,

Rod

Well

column was definitely dead. Get nice sharp peaks with new column.

Well - you've just re-proved why it sure helps to have a brand-new column sitting in the drawer underneath the GC - saves a ton of troubleshooting time !!!

"Sell" that idea to your boss, that all it "costs" is ONE extra column for the lifetime of the assay.

Chromatographer tried everything you said, was still getting horrible peaks...then realized i wasn't hearing a clicking sound...The purge valve wasn't turning on at method start arrrgh!!! classic rookie mistake... problem solved...nice clean separated peaks now....

thanks for all the help!