Chromatography Forum

When you have a mixture of glycols, glycerin and water, which do you think the best chromatographic method to identify the glycols?

Either could work. GC would probably require derivatization, which is a pain in the nether regions. LC would have detection limit issues (no chromophore).

Pulsed amperometric detection works perfect for glycol and similar alcohols.

GC with trimethylsilyl derivatization, non-polar DB-1 or DB-5 capillary. Dilute with DMF, transfer some to autosampler vial, mix in derivatizing agent, cap and shake, inject into GC. The reagent will also react with any residual water, so make sure to have excess reagent.

This has worked well for me for 30 years, helped put my two kids through college.

GC with trimethylsilyl derivatization, non-polar DB-1 or DB-5 capillary. Dilute with DMF, transfer some to autosampler vial, mix in derivatizing agent, cap and shake, inject into GC. The reagent will also react with any residual water, so make sure to have excess reagent.

This has worked well for me for 30 years, helped put my two kids through college.

Hi cpg,
about Deg (diethilene glycol) and trimethylsilyl derivatization what're the best gc-fid conditions? I m trying but can't see the peak of derivate product. My temperature set go from 80ºC to 300ºC (inj: 300ºC) , end time is 30 minutes with a 30meters non-polar column. Any help? Thanks!

Glycols and diols can be easily done with GC. Derivatization is not required. Best selectivity and peak shape for diols is obtained using wax columns like Rtx-Wax. If water is the matrix, the injection will be the biggest challenge. Glasswool will be a challenge, so best use a liner with higher surface like cyclosplitter. Some like the inverted cup. Double gooseneck works, but reproducibility is not that good. If you can use hot-needle injection, use that, as it's the best for such samples.

To reduce the impact of (big)water peaks on chromatography, try to do the analysis at higher temperatures, using thicker Wax films. 1 micron on 0.32mm ID will do.

Jaap
Restek corporation

Thank you jdezeeuw, very interesting! Matrix is seawater so like you said implentation of a direct injection maybe hard and i need to use the gc we have "without spend too much time or money" (my boss words, so no new column). So i was trying derivatization, we have only 2-3 samples every year so i don't mind losing few hours in it. Only problem is dryness the sample before derivatization. There is something else that i can use in aqueous solution?

P.s. This morning i see my peak! very small but it made my day!

Hi Jaap,
Can you point me towards some more information on the Restek non-derivatized method? I'm looking for ethylene and propylene glycol in aqueous samples-but will be running several hundred per week.
Thanks,
B

[quote="jdezeeuw"]Glycols and diols can be easily done with GC. Derivatization is not required. Best selectivity and peak shape for diols is obtained using wax columns like Rtx-Wax. If water is the matrix, the injection will be the biggest challenge. Glasswool will be a challenge, so best use a liner with higher surface like cyclosplitter. Some like the inverted cup. Double gooseneck works, but reproducibility is not that good. If you can use hot-needle injection, use that, as it's the best for such samples.

To reduce the impact of (big)water peaks on chromatography, try to do the analysis at higher temperatures, using thicker Wax films. 1 micron on 0.32mm ID will do.

Jaap
Restek corporation[/quote]

With the information given I would prefer to use HPLC if I were doing the analysis.

But good luck in any case.

Rodney George