Surfactant Impurities

[aprilcparker]

I am trying to analyze some surfactants using an Acclaim surfactant column. However, the impurities (Glycerine, Sodium Monochloroacetate, DMAPA, and Sodium Methylate) are all eluting around the same retention time before 3 minutes. While running my standards they are easy to identify, however when running the sample solution I am getting a co-elution of peaks. Are there any suggestions you could make to get the impurities separated and increase the resolution in my sample solution. Thanks in advance for your time and consideration, I look forward to your reply.

Just to let you know, I have tried different organic modifiers such as ACN and MEOH and different precentages ranging from 10%-70% and different pairing agents such as Ammonium Acetate and Triflouroacetic acid, using pH ranges from 2-6 and none of them have given me acceptable resolution.

If any additional information is needed to for this analysis, please let me know.

[HW Mueller]

Is that Na methylate a typo? What is DMAPA?

[aprilcparker]

Hi, DMAPA is Dimethylaminopropylamine also, Sodium methoxide, is commonly called sodium methylate. Sorry for the confusion. Thanks for your reply

[SIELC_Tech]

There is no way to retain Glycerine, DMAPA, and Sodium Methylate on Acclaim Surfactant column. Your impurities are hydrophilic neutral or basic in nature and there is no mechanism to retain them on this column. You can design a method for everything except glycerine on Obelisc R tri-modal column (RP, cation- and anion-exchange), but glycerine will come on a void. Alternatively you can use Obelisc N and retain everything by combination of HILIC, cation- or anion-exchange.

[HW Mueller]

The reason for thinking the methylate was a typo is that there is no such thing in the presence of water.

[aprilcparker]

Thanks for your responses

@ Siltech

I was able to detect the impurities using this surfactant column, because it has RP, and ion exchange properties. When I inject them as individuals, they give me a very sharp and symmetrical peak with great chromatography. The only issue comes when i'm running my sample the peaks co-eulte because of the retention times being so close. DMAPA elutes at 1.86 minutes, SMCA elutes at 2.11 minutes, and glycerine elutes at 2.62 when injected individually.

@ HW Mueller, you are correct, NaOMe can not be present with water, however it is added in the reaction as a catalyst and it's suppose to be all converted to MEOH, and I was trying to prove that it had all been converted during this analysis. That impurity is not as important as the others, I was trying to optimize this method and detect as much as I can within one sample prep and one set of chromatographic conditions, however I'm noticing that this may not be able to do. Or that this analysis may be better done by titration. Thanks for all of your input.

[Consumer Products Guy]

I am trying to analyze some surfactants using an Acclaim surfactant column.

April - can you detail what surfactant you are trying to analyze? I've been working with surfactants 35 years and have never run across such a mixture.

[aprilcparker]

The surfactant is Cocoamidopropyl Betaine (CAPB)... We are using an amidoamine (CAPA) to make the the betaine, and producing the CAPA here in house as an intermediate. My goal was to determine the amount of free DMAPA in the CAPA, and determine the glycerin in the final product. Or if possible detect both of them in the final product. I am getting 3 peaks in the CAPA analysis which i have determined to be the DMAPA, Glycerine, and the actual amine (not yet confirmed) but by process of elimination and spiking of the peaks I have confirmed the first two peaks as DMAPA and Glycerin. They separate in my intermediate but not in the final compound.

[SIELC_Tech]

waterbury Company (Sean LeTrad) had the same task, there is discussion on Chromforum on analysis of quats and glycols. He ended up using Primesep D column with derivatization of glycols.

[Consumer Products Guy]

We buy and use CAPB, but we typically assay for the glycerin by GC (HP-5 capillary, BSFTA derivatization), solids, and NaCl by titration before use.

Do you have a decent way to assay for CAPB in a finished product that you can share? Thanks.

[SIELC_Tech]

I assuming that your first peak comes pre-void, as you probably use 250 mm column or reduced flow rate on 150 mm column. When you have a mixture peaks will come close. Anything extra will mess up your analysis, but. I guess that thismethod is okay with you. My rule is to have k' of at lleast 2 and resolution of at least 2. You have none of these and it might come back and bite you.