Chromatography Forum

HI,

I'm trying to determine a high boiling glycol (BP of about 230 deg C) from the PEG 400 matrix. I have tried the capillary column (ZB 1) so far. The standard glycol solution in dimethylacetamide gives a good %RSD, but when the glycol is spiked into the sample matrix containing PEG 400, I don't see the glycol peak.
The GC conditions are as follows:
Injector temp = 300 deg C
Detector (FID) = 300 deg C
Oven = 90 deg C for 3 minutes, ramp @ 10 deg C to 210 deg C hold for 3 minutes
ramp @ 20 deg C to 280 deg C hold for 10 minutes (Total run time = 32 minutes)
Injection volume = 1 microliter, split ratio 1:1
Flow rate = 4 ml/min, make up = He (25 ml/min)
Can anyone help me?

Thanks.

R

You have demonstrated the effect of the difference in matrix upon the vaporization of the glycol.

My suggestion is to dilute the sample with a silylating reagent to make the glycol more volatile.

This could reduce the effect of the PEG400 enough to allow the elution of the TMS-glycol, or not.

You may have to perform RI-HPLC in order to measure the glycol properly.

good luck,

Rod

Do you mean PEG with 400 EO, or a PEG that is about 400 MW? I've seen a ton of people confusing the nomenclature. The first would be a solid (maybe without your glycol) where the second is a clear liquid.

Anyway, from my experience, I would've started with what chromatographer1 stated, and not even tried without derivatization.

I'd start with DMF as solvent, personal choice. You can start with the same capillary column you already have. Don't make stuff to concentrated, as you want to minimize any contribution form the big PEG.

Hi,

The sample matrix is PEG 400 (liquid). I have to determine the glycol (which is an impurity in the sample). The sample cannot be diluted further since I have to determine the glycol which needs to have recovery and sensitivity at the LOQ level at the existing finished product sample concentration. I don't see the glycol peak when this impurity is spiked in the PEG 400 matrix for the range/recovery study. Is it that the PEG 400 is not completely eluted from the column at 280 deg C and somehow being carried over into the next subsequent injections?
Any suggestions?

Thanks.

R

Is it that the PEG 400 is not completely eluted from the column at 280 deg C and somehow being carried over into the next subsequent injections?
Any suggestions?

Possibly. I'd derivatize and go to high temperatures to clean out the column well before my next injection, a good procedure when looking for low levels of anything.