Chromatography Forum

Does anyone know how is the degree of esterification on the FFAP (Nukol) columns? I mean, all the free hydroxyl groups from the PEG are esterified?

Thanks,
Fabiano

The terminal hydroxy functional groups are nominally esterified but with the introduction of water or other alcohols onto the columns it is possible that the esterification reaction was reversed and the free -OH and free acid were formed.

I know of no method to determine the free OH content with so many free acid groups present.

Why, pray tell, and how, does this affect your analytical problem?

best wishes,

Rod

I was injecting (because of laziness in the beginning) an acetylation reaction without dry, and the column ( a 5 M FFAP) withstood very well until now, for 200 injections.
The first thing I imagined was that the anhydride would acetylate my free hydroxyl and I would have not retention or skewed peaks, but until now it is very OK, RSD 0.8%.

I'm wondering if I keep doing this and if any other column would resist in the same way to acetic anhydride.

There are no free hydroxyls (in a new column) in a FFAP so your concerns are unfounded, unless of course, you do get hydrolysis from water in your sample or carrier gas.

But if you also have acid anhydrides they would likely react with any free hydroxyls you might have available on the column, in essence, you are rederivitizing your GC phase.

If you are having problems with the column after 200 injections of an acetylation reaction mixture, well, gee, I think you got your money's worth.

Worst case, try rinsing the column to clean it of contamination.

Best case, replace the column.

best wishes,

Rod

Way back when, I used to acetylate lipids ( acetic anhydride/pyridine ) and inject 1:1 toluene mixture onto a 5m 0.1um methyl silicone 0.1mm ID column to measure mono, di, and triglycerides in 15 mins.

I used to run hundreds of samples with minimal column degradation ( polyimide outer coating hardened, and columns tended to break well before peak separation was affected ). In my experience, acetylation reagents were cheap and very effective for neutral lipids.

If you can obtain sufficient separation with a low polarity silicone phase, you may find longer column life, but I'd also try cleaning your column first, and perhaps also ensuring that the degradation isn't due to oxygen.

Bruce Hamilton