Injection of Aqueous Surfactant Samples

[adam]

Hello

Has anyone had any experience injecting aqueous surfactant solutions (the surfactants are not the analytes, they are in there for another reason).

Let me explain better what I'm asking. We all know that, in reversed phase, you can generally inject larger volumes when the diluent is water, as compared to ACN or Methanol, etc. So I am wondering if one is injecting aqueous surfactant solutions, would the presence of the surfactant have the same effect as if one was injecting with an organic diluent like ACN or Methanol.

Has anyone had any experience with this? And, if so, could you kindly share what you've observed?

Thank You
Adam

[Rndirk]

Do not add surfactants deliberately in liquid chromatography. We run an LC-MS environmental analysis with cationic surfactants as analytes, that stuff is virtually impossible to get out of your system.

That said, surfactants are a very diverse class of compounds. I can imagine situations where they influence the peak shape of the analyte for sure. I wouldn't compare them to organic solvents.

[Kenn]

Hello

Has anyone had any experience injecting aqueous surfactant solutions (the surfactants are not the analytes, they are in there for another reason).

Let me explain better what I'm asking. We all know that, in reversed phase, you can generally inject larger volumes when the diluent is water, as compared to ACN or Methanol, etc. So I am wondering if one is injecting aqueous surfactant solutions, would the presence of the surfactant have the same effect as if one was injecting with an organic diluent like ACN or Methanol.

Has anyone had any experience with this? And, if so, could you kindly share what you've observed?

Thank You
Adam

No the surfactants won't act like CH3CN or methanol. Yes I have analyzed them, typically in spray solutions for residue or plant studies. the solutions sprayed in the field typically have surfactants in them to make a better carrier for the analyte. These solutions must be analyzed to confirm the concentrations in the tanks. Those concentrations are typically very high so I dilute them as much as possible and shoot as little as I can depending on sensitivity and they do not pose a problem. As far as sample composition strength though no, I would consider the surfactant fraction to be part of the aqueous because unless for some reason they added some organic to it, it is aqueous. For all practical purposes it is soapy water.
However, I'm running LC/MS/MS and don't remember if they were a problem in the UV with absorbance.

[Consumer Products Guy]

We injected samples of liquid soaps and detergents into HPLCs for 3.5 decades before I retired. You will not get an effect similar to injecting a large volume of strong solvent.

Typical preparation when looking for actives in commercial liquid soap samples was 5% sample in solvent, with the surfactants remaining in solution.

When we assayed laundry detergents for nonionic surfactant content, we used even higher concentrations (and the anionic surfactants stayed in solution).

Note that these assays were either HPLC-UV or HPLC-RI, not HPLC-MS.

[DoryFish]

Hi, I'm not sure what concentration surfactant you're working with and whether what I'm about to say is so basic that it's of no help, but here goes. Recently did a project with thyroxine and the USP dissolution medium contains 0.2% sodium lauryl sulphate. The presence of SLS caused thyroxine to elute about 1 min later with a 10 mcL injection. I also had to do five replicate injections of the blank (no API but with SLS) to get a equilibrium "concentration" of SLS on the column so that all subsequent injections gave a constant retention time for thyroxine. Larger injection volumes distored the peak shape.