Chromatography Forum

I need to analyze ethoxylated nonionic surfactants but we only have GC-FID and HPLC-UV in our lab. i tried DB-1 and DB-5 column but no success. Any suggestions? thanks in advanced

Your molecular weights might be too large to use GC.

You can try negative absorbance HPLC with the correct UV absorbing mobile phase.

You might wish to try TLC. Not expensive and easy enough to use.

Do you have the structures you expect in your surfactants?

Good luck,

Rod

thanks and it is linear C11O(CH2CH2O)7H

That is a pretty heavy molecule to elute as a free alcohol.

Time to Silylate or esterify.

I would silylate and prepare a TMS ether on a 5% Phenyl 0.25µm or 0.5µm film column. Expect high oven temperatures above well 300°C.

OR

Derivatize with a UV absorbing functional group and use HPLC.

Good luck,

Rod

thanks and it is linear C11O(CH2CH2O)7H

Undecyl alcohol ethoxylate assay is straightforward. Dissolve in DMF, add BSTFA reagent, shake, use either DB-5 type capillary or specialty high temperature capillary.

Thanks, CPG.

Your broad experience is always a great help on the Forum.

Rod

thanks and it is linear C11O(CH2CH2O)7H

Undecyl alcohol ethoxylate assay is straightforward. Dissolve in DMF, add BSTFA reagent, shake, use either DB-5 type capillary or specialty high temperature capillary.

thanks. I tried with injectior inlet temperature of 300 C and oven temperature up to 325C using both DB-1 and DB-5 but no peak was observed. Any suggestion for the temperatures?

How much reagent did you add?

Rod

thanks and it is linear C11O(CH2CH2O)7H

Undecyl alcohol ethoxylate assay is straightforward. Dissolve in DMF, add BSTFA reagent, shake, use either DB-5 type capillary or specialty high temperature capillary.

thanks. I tried with injectior inlet temperature of 300 C and oven temperature up to 325C using both DB-1 and DB-5 but no peak was observed. Any suggestion for the temperatures?

Yes. Your temperatures are not the issue, they are fine. Look elsewhere. You will see solvent peak(s) then multiple peaks in a bell-shapped gaussian-type distribution.

Start with the basics. Are you getting a solvent peak? Did you try first a more-concentrated sample? Is your needle bent or plugged?

Hi CPG:

This is my first time test surfactant and my only experience with GC is residual solvent test. I really appreciate your help.

I did see solvent front peak and multiple peaks with bell shape when I injected at very high concnetration( I was looking for a single peak).

Does this mean I will not see a single peak, but multiple peaks for the injection of C11O(CH2CH2O)7H?

This method will be used for equipment cleaning and the concentration level is very low (10 ug/mL to 300 ug/mL). Do you think GC-FID is a good approach to quantate C11 at this level with the presence of Ethoxylated, propoxylated alcohols C8-10 and C13-15?

Many thanks

I did see solvent front peak and multiple peaks with bell shape when I injected at very high concnetration (I was looking for a single peak). Does this mean I will not see a single peak, but multiple peaks for the injection of C11O(CH2CH2O)7H?

You will get multiple peaks. If the undecyl alcohol starting material was relatively pure before it was ethoxylated, then you will see a peak from C11O(CH2CH2O)2H, one from C11O(CH2CH2O)3H, C11O(CH2CH2O)4H, etc. If the parent alcohol chain was a mixture before ethoxylation, things get more complicated, but the peaks elute well, and in a set order.

This method will be used for equipment cleaning and the concentration level is very low (10 ug/mL to 300 ug/mL). Do you think GC-FID is a good approach to quantate C11 at this level with the presence of Ethoxylated, propoxylated alcohols C8-10 and C13-15?

No. You will need to concentrate your sampless. The ehoxylated, propoxylated alcohols C8-10 and C13-15 will all elute in between the undecyl alcohol ethoxylate peaks.

If you are trying to verify that your rinse water is "free" of nonionic surfactants for equipment cleaning, post that question.

CPG:

Will do and you are a great help here.